There isn't really a coherent RX600 groupset.
Basically GRX is a glossy re-marketing exercise for a bunch of different parts from different sources
The RX400 rd is a repurposed Deore T6000 and designed for 32-36t cassettes. It would shift both 10 and 11 speed road perfectly but it's not a good choice when you hope to fit narrower cassettes, it's much more towards the MTB/granny gearing range.
Rd-Rx812 is based on the Deore t8000 and it works with large cassettes in the 11-40 or 11-42 range
Rd-rx810 is officially rated 11-30 to 11-34. It has the 13t jockey wheels Shimano has come out with for their latest stuff to drive sales with the cult of the new. It's not quite the same as the rd-rx800 ultegra Rx rd, which is arguably higher quality being all aluminium instead of using plastics. Rx800 uses the same derailleur cage as r8000, and both rx800 and r8000 are rated 11-28 to 11-34.
It's likely rx810 is ok for 11-28 too for this reason
In terms of wheels, nominally all road disc hubs are 5mm wider than rim hubs used to be. Shimano didn't bother updating the road chainsets though I think SRAM do. So it was a selling point that the grx chainrings are moved out to where they should have been in the first place....
Anyway this means that chainline is actually quite flexible in that you can increase hub width without moving out chainrings in most cases except on very compact framesets, so nothing too much to worry about there. I wouldn't trust different freehub models to have the same dimensions, not even necessarily two by the same company. So ideally you'd measure this yourself when purchasing the wheel.
I don't think the different cassettes will itself cause an issue - it would be the different freehub measurements.