They... would look silly if they tried this, yes! While Lue Nun won't oppose Zevran's attempts to flirt with her, she won't believe he's serious and would not fall for his advances anyway; Se and Viv know this about her and have lived/worked with her for a long time, so they would not be fooled by a polymorph.

If your group would like them to try this anyway, Se and Viv would be suspicious of the group from there on out, and would insist Lue Nun dismiss them. She would not, but interacting with the women would get them nowhere after that point. If you choose this option, your group will have to make a judgment on the NPCs based on what you have already learned.

Because this answer is essentially "no, sorry" with no new information, you're welcome to try one more time!