"Hey Googlette, you look really good in a bathing suit" is a comment about how the woman's body looks in a revealing outfit. I'd say this is generally unprofessional, though in some contexts (perhaps she'd just been expressing a lack of confidence in her body), it could still be appropriate.
"Hey Googlette, that bathing suit looks really good on you" is a comment on the particular bathing suit and how the combination works well. It's potentially more of a comment on her good choice and fashion sense than on her body. If the bathing suit is particularly risqué then it might be inappropriate but if it's just a normal bathing suit I don't think it'd be any more inappropriate than "your new haircut looks really good" or "is that a new top? It looks really good".