I haven't had my WLS surgery yet but to be honest, braids during my surgery is ideal. I say this because I had a hysterectomy a couple of years ago and had my hair in long senegalese twists. I remember worrying about my twists being a problem but I just threw it in a bun at the top of my head and had absolutely no problems -- it never got in the way and I was in the hospital for 3 nights.
I think that as long as you're able to put it up, you shouldn't have any problems at all during your hospital stay.
Best of luck on your upcoming surgery!