Pretty sure I’ve used XLR out and recorded a mic on the cab at the same time. I can fire mine up and test that again. I will go do that now and edit my reply.
Edit: As I thought, you can definitely use the cab sim and the speaker/cab at the same time. Luckily I didn’t put an XLR cable into storage. I did not test balancing channel volume with XLR output levels, it was a quick test.