You may be right, code-wise. I'm really not sure. I'll likely have a drop ceiling so the plumbing will be "accessible" even if wrapped/encased in something. If if fails it's not as though it'll be a huge mystery inside of a wall somewhere that's been filling with mold for years. Someone (likely me) will just have to remove a ceiling tile and will immediately have access to the problem.
BTW, using the union joint wasn't just me being lazy - it was the only good way to maneuver the parts for gluing at the perfect angles given the clearances I had.
And before someone tries to call me on it: yes, my vent for that 2" p-trap is pushing it, distance-wise, but the plumbing has been working great for over a year now. The first thing I did after finishing the plumbing was flush the toilet and watch the water in the shower p-trap: didn't budge.