There is one of the Ape Rescue centres in Africa that has(or had) a female believed to be a Cross River Gorilla. Perhaps someone can remember which one it is- Limbe?
As Cross River Gorillas are virtually indistinguishable, at least superficially, from Western Lowlands, any that have left Africa and entered zoos in the past have presumably gone unrecognised.
I suppose anything was possible in the past and that animals from the Cross River Gorilla's range might have entered captivity and even have been bred with other Western Gorillas.
However I don't know whether enough scientific research has been done to reliably distinguish the DNA of these two species, or indeed to identify just how seperate they are from each other. So I imagine the queries you raise will probably remain unanswered.