#1. Vegeta is NOT GAY.
Second of all, Piccolo is weaker then him.
Now, I don't have anything against the green guy but the fact is he was rarely stronger then the Vegeta.
He was stronger after his Nail and Kami fusions for a short time but was quickly surpassed again.
For 99% of the series Vegeta was always stronger, usually much much stronger.
So no, Vegeta would not have sex with Piccolo and Piccolo could not force himself on him.
Also Namekian's don't have sexual genitalia.
They reproduce by laying eggs or some shit from their mouth so it is impossible to begin with.