I had a pair, and sometimes one of the pair would disappear into their bolt hole for days or even weeks. That's the ONLY evidence I ever had that there may have been spawning going on. Setting them up in a breeder tank with easily removeable pots & pipes would work better for observing than a full blown reef tank like I had my pair in. FWIW, a sand substrate on the bottom may be helpful. Look up related fish too, like the "Scissor Goby".
Matt