Safe to use pressure cooker for beer stew?
It is perfectly safe to add beer to any recipe in a pressure cooker. (well, any recipe you might use beer for outside a pressure cooker). While I've not done this with rabbit I have with venison (for chili), beef and chicken for various stews. 

Assuming your concern is adding a 'carbonated' beverage, this question has been answered here: Carbonated Beverage in Pressure Cooker

Indeed one may easily find a plethora of beer in a pressure cooker recipes like these.