I have a seed card, but I don't want to store all my coins in one account with one seed. I want to spread out the risk.
You may should think about how you are spreading the risk.
I don't really see a reason to buy a second HW wallet. Im not even sure if thats more secure than only having one.
I understand why you wouln't want to keep all of your coins on one address. But 1 HW wallet is
enough.
You must think about the threat you are exposed to. If you fear from getting malware on your pc.. then 1 ledger is as safe as 2 are.
If you fear of someone cracking your private key.. there is also no difference between owning 1 or 2 ledgers.
In case of a fire both get destroyed. (Yes, you could store them seperately.. but you also could do this with our seed-sheet)
The only case, i see, where 2 ledgers would be better is when you get robbed. In this case you can hide 1 and only give up the other (seed or device).
So, is it possible to use two Nano S Ledgers with two separate accounts?
Of course. There is no reason why this shouln't be possible.