Amphibious Minion ~ Elite Skill
He doesn’t have underwater animations that’s the only reason he doesn’t work underwater. Back in beta he’d just kinda walk underwater while floating.
It seems they are increasing somewhat the underwater support (new aqua breather announced, more support for underwater weapons in the specialization lines etc…), so it does not seem unlikely. To be honest, the flesh golem case in particular is really easier to fix than some (there is not intrinsic thing in it that cannot work underwater).