I think it should be OK to start training. You'll probably be doing alot of squat, lunge, sprawl type activities. Start slow and see how your leg feels. Also let your coach(es) know and get their input.
Depending if you have a focus, you might want to start with a stand up game (Kickboxing etc..) and go from there. My biggest concern would be grappling some of the leg locks (heel hooks, toe holds) that can put alot of pressure on your knee. If you do grapple mention this to your training partner. Almost all the people in this sport are cool and will appreciate your letting them know.
Good luck and have fun. This sport is a blast!!