I am certainly fine with the idea of them having Chem Geld. I guess it does represent something slightly more than what they go through, but I had always taken Space Marines having no sex drive what-so-ever (chaos worshippers aside). They would still have the external equipment, but the whole subject matter doesn't interest them (if they even know about it).
I can accept that many of them would still be affected by some of the things that Chem Geld protects against and I don't think the insanity point is really suitable in their case, but that actual seduction would have no effect sits fine with me.