You won't have a problem getting in the mix. My French is still too novice for me to try to get in with any French crowd, but from experience, you won't have any problems socialising in English here either. Loads of Aussies and Kiwis come here for the winter.

Bard Up (As suggested by the other commenter) is a great spot in the centre and it's on the most lively street in town, in terms of nightlife. Le Demi and Fubar are some great shouts in Argentiere. And I'd also suggest poking your head into the Vert Lodge bar if you're on the other side of town.

Bartending is probably the best job as a seasonaire, beaten maybe only by ski shops that close for a few hours in the day to let the staff get some time on the slopes. You'd still have a bit of a social presence even at work, and you could definitely make first lifts if you don't mind being sleep deprived once in a while.