Its probably more than ok. I mean hell, i have put sheet vinyl on top of OSB sheathing panels in my own house.... just because you shouldn't does not mean you cannot. If what you have is available and already done, well i can tell you i wouldn't be changing it.
There is a whole slew of best practices, as a tradesman i follow them to the letter lest i get burned and own a job. Then there is the "this will most likely be ok" side of things that we all know will be fine by i cannot sell it to you because someone once said "there is a better way".
Here in my own house, i have fibersheet flooring installed on osb, over an unconditioned crawlspace in an unconditioned room. Going on 5 years now and it is still rock solid, that room has been flooded numerous times whilst i was mixing salt water for my fish tanks... its amazing how often you can fall asleep while making RODI water in a barrel... flood. Its where we wheel barrow wood into the house to burn..... you get the idea, abuse. That floor still looks brand new.
I am thinking in such a small space, just roll the dice with what you have.
With a BC panel, you will more than likely have to do some patch work to get the face smooth enough for a sheet vinyl or glue down plank however, and that is where it gets ugly. The moisture from patch has a tendency to raise grain on plywood, which then leads to more sanding... but it is all possible.
