You should not use copies of the same wallet.dat simultaneously on multiple instances. The wallets create a new set of keys from time to time, and two different copies end up unsynced from the keysets so that you might be missing balances from some of the wallets even thou the coins are there. This goes with all bitcoin-qt based clients and their wallet.dat:s, not just USDe. It might work just fine for some time, but probably not forever and not worth the risk.
EDIT: ONE WALLET PER ONE DEVICE AT A TIME!
So does that mean that it's ok to use the same wallet.dat file on multiple devices as long as it's not done simultaneously?
Not entirely, if you switch between two copies that you frequently use it's as bad. Only situation when a copy of the same wallet should be used is when restoring a backup and the other copies of it will no longer be used on other installations.
Understood, thanks for the info!
No problem, happy to help people keep their beloved coins secure...
And if someone might end up with wallet copies with unsynced keys it's not unrepairable, but it's not too easy or fun to repair either. So better just to avoid causing it in the first place.
I first ran into this when I wanted to use the same wallet on my mining rig for solo mining and on my laptop for spending those mined coins more easily. And the advice for not to do so came from Gavin Andersen (bitcoin-qt core dev). Method of recovery is extracting all the keys from all the corrupted wallets and then inserting them "manually" to a new wallet. Tool for extraction is dbdump.py and can be found at
https://github.com/gavinandresen/bitcointools