That might have worked. Who knows, she might have even considered it. But she probably figured that if she had openly revealed herself as a Cardassian, it would have made her a target for assassination by the Maquis on the ship. She couldn't afford to take that risk.
The Maquis are lazy. They'd rather fight a war than pack up and box up their shit in the attic and freight it back to Earth. How many assassination attempts did Paris have to fend off?
But Seska would assassinate someone if she had reason to, or for revenge so she may see being on that crew as a revealed Cardassian to be far less safe than it actually was.
She did apparently enjoy spending her free time rewriting a holodeck program to torture Tuvok just because he potrayed her in a less than flattering(yet very accurate) light. She even worked in some C/S into it fanfic style! Not sure how she ever would've expected to get away with that if Tuvok had accessed that program while she was still on board, but long term strategy doesn't appear to be her strong suit.
Most of the Maquis probably just saw Paris as comic relief. Chakotay was plenty pissed off at him, but wouldn't try to kill him. Chak was a real Starfleet officer before he defected, after all. However, the Maquis - with their inevitable racial prejudice against Cardassians - would naturally focus all of their hatred on any Cardassians they found, up to and including Seska. If she had openly admitted being Cardassian right from the start, she'd have been dead in a week.
No she wouldn't. They were all either wimps or too intelligent not to realize their cause was dead in the Delta quadrant and so no longer worth dying or spending 70 years in the brig for. The only one who might have killed her would be B'Elanna but by that time she was in good with Janeway and wanted her respect so it wouldn't have happened.
Seska would have already had sex with the most hateful racists on the ship. Made them fall in love with her, or at least eager for another booty call, and after they found out who and what she really was would have resulted in a series of conversations similar to this... "You my hate my spoon, but you love my pussy... Although can you imagine what it's like to screw me in my spoon? Aaaaaaand now you love my spoon. Perfect. So, fuck off."
When a telepath says "I killed him because he was looking at me funny" it's not such a bullshit excuse.