my male robo seems to be sniffing/biting my female robo and yes i have them in the same tank and they do sleep together without problems (plus i have 5 inches of bedding so they can hide/dig wherever but choose to stay together), it's only at night time when he has that urge to chase her down and force his nose into her vaginal area. she squeals when he does this so i assume she is getting bitten but there are conflicting answers online as to whether or not they are playing or fighting (no blood drawn)

if it helps, in their nest together underground the bedding, he does slowly sniff her and what not but she usually just pops up and basically tells him no
+ she does not fight back beside going on her back squealing facing the male hamster, run away, rest, repeat