I painted smooth cedar rails (2 X 6) along with 6 X 6 posts to contrast with composite flooring. My experience is that if the caulking is thorough and a quality paint is used, paint is good. If the caulk is shabby, water will reach the wood and you're dead. Keeping it clean will apply to any material. Cedar is very stable, doesn't twist. Pass this on to the boss, and enjoy the project.

srercrc is going to think I am picking on him but I wouldn't use cedar if you are going to paint. New growth cedar is horrible with respect to rot. A small amount of moisture will rot it right to the core (and quickly). Why not use the cheapest material (PTP) and properly prep and stain it with a solid. Solid stains offer breathability whereas paint does not. On verticals you should be fine with keeping it clean and maintained like sre recommended. I would guess every 4-5 years you would need to recoat.

No offense taken, PP. I guess in my limited experience I haven't seen the problem you speak of. All the trim on my ten year old house has painted smooth and rough cedar...the only problems I've had is where the caulk cracked and started rot. I'm a little surprised you're recommending PT...it moves to wherever it wants to go.

The key to using PTP is to 1) get KDAT pressure treated lumber from a lumber yard as opposed to HD or Lowes and 2) get it treated as soon as is possible.