Actually, no. Ash's Pikachu was confirmed to be male in a Diamond and Pearl episode. Admittedly, he was already designed like a male Pikachu, but he was like that before Gen IV created those gender differences...
I don't really like how they wrote off pee-wee in "just for sidekicks." I think having spike raise him would have been good for spike and the show, give him more to do when not with the mane6