No problem! Re Gravelords as Vampire counts specifically:
Zombies: these guys rank up on 25mm squares without any trouble and look great, provided you like the 'grown through with roots' and carrying the graves they were staked down to around on their backs' aesthetic gimmicks. Again, GW couldn't just give us plain zombies because they sell their models on extra detail. I like the roots but not so much the staked graves on the backs (fine with that bit in AoS but it doesn't look right ranked up imo), so I left those bits off and the models mostly work without them. the ones meant to have that stuff on their backs are a bit flat and hunched, but not unworkably so, and there are spare root and stake bits to fill the holes that the graves are supposed to peg into. I did use two of the back-graves though, one with a little bell to be a musician ad one with a stake that I trimmed off and pinned a polearm from the corpse cart kit to as a standard bearer.
Skeletons: their tattered swirling skirts and akimbo weapon and shield posing, particularly if you want to give them spears (arguably a waste of points in the current rules, but that could easily change in the future), can make these guys tricky to rank up, though it is possible to do so. Personally I prefer the look of the old 7th/8th edition vampire counts skeletons if you already have them or know somebody with a bunch of them burried in a closet that you might be able to trade for. Unfortunately, you can't just buy the old vamp counts skeletons, and the even older tomb kings skeletons look a bit goofy imo. I'd recommend third party skeletons - there are many to choose from, but if you want to play in official GW stores or events then the soulblight skeletons might be your best option, and if so just be careful to rank them up as you assemble them to make sure they fit together in the formation you want. Start by tacking them down with just a tiny bit of glue on one heel in case you need to re-position some of them later, and then go back with a bit more glue once they're all good.
No picture since, again, I use the old vamp count skittles, sharing the same unit/models with my tomb kings.
Black Knights/Hexwraiths - back in the day these guys fit very badly on 25 x 50mm bases (especially since GW cav bases were actually closer to 23.5mm wide). I actually had to trim their cloth barding to get them to rank up next to each other. They should be much happier on the new 30x60mm heavy cavalry bases for old world, though I haven't put any on the new bases yet to speak from experience. I don't have a picture of these atm. Unfortunately, this kit is perpetually out of stock from GW. Be prepared to pay like double on the secondary market, or sign up for GW's terrible email notification scheme and hope you notice the email and are able to make the purchase in the like one day they'll be back in stock every six months or so.
Blood Knights - while they are a fair bit larger than the black knight models they still fit well on 30x60 mm bases, at least horizontally, at least if you give them lances or are careful positioning the swords. The champion's mace arm, sticking way out to the side, will need to be either cut off and repositioned or you'll need to give them a lance or sword instead. You can still use the cape from the mace arm if you cut off the arm and trim the inside shoulder of the cape. While they fit ok side to side, their horses are very long, and they won't want to fit into multiple ranks. Fortunately they're better off in multiple small units rather than one deep one, so it shouldn't be a problem.
I don't have pictures for the dire wolves, but they fit fine on their 25x50s, though the champion's tactical rock is a bit wide.
I haven't put the new fell bats on squares, but they should fit fine & look great, worlds better than the old ones.
the current AoS Crypt Ghouls are the same models as the old fantasy crypt ghouls, and will fit better on 25mm bases than they used to on 20mm bases. Crypt Horrors, Vargheists, Corpse Carts, grave guard, spirit hosts, wight king on foot, Zombie Dragon/Terrorgheist, Coven Throne/Mortis Engine, Necromancer, Banshee, & Cairne wraith - that stuff's all old models too.
The current Vampire Lord on foot is made for a 40mm round, and will have difficulty ranking up in a unit of 25mm squares. Plenty of 3rd party alternatives out there, but if you're looking for a 1st party legal option that fits better, look for the Crimson Court warband from Underworlds/War Cry.
No official bat swarms in the Gravelords range, but iirc there's a middle earth option for that, and if you can find them the Cursed City box had bat swarms.
The Mounted Wight Lord is big & their horse has a spread out pose. I haven't tried to put them on a 30x60, but they might struggle to fit, so you might be better off converting a wight lord from a Black Knight model. There is no GW official vampire lord on steed model currently available. If you can get your hands on the old Mannfred von Carstein model he fits well enough on the new bases (see above), otherwise you might have to convert from the current Blood Knights, or again there are plenty of third party options.
