By definition they are two separate species and therefore should not be able to interbreed and produce fertile offspring.
However, there isn't much information on Brachygobius. Most people can't even identify them. So, I have no clue if it would work or not. If it did, and the offspring were fertile, then you'd have proven that those individuals and whatever you bred them with were the same species.
Do you already have BBG's besides these? Comparative pictures might help.