Mark might have a better answer for this than me, but I personally wouldn't be concerned about it per se, though I would be prepared for a potentially unpleasant experience. I continued to try and smoke pot occasionally for the first few years after my injury, and my usual experience was that my brain would just completely go to crap (or "pot", if you're into puns) whenever I tried the stuff (or was in a room with a lot of the smoke around). My short term memory would get completely shot, I'd get really anxious, I couldn't elucidate my thoughts well at all... it was just really unpleasant (and yes, I realize these things happen to pot smokers sometimes without PCS, but they were far more acute, abrupt, and overwhelming with the brain issues in tow, I can assure you of that).

Basically, it was awful and the lulled mental fog that an uninjured pot smoker might expect to experience the next morning would last for me for a couple of days, but beyond that I felt fine. I don't think being around it it will hurt you in the long term, but it might well put you in a crummy place for a few days so I'd recommend avoiding it if that's at all possible.