Ice ice ice. Then when you've finished icing, more ice. No heat. If he needs to do heat, make sure he uses contrast therapy (cold following hot.)
Inflammation of the bursa is a common problem with ball players, also (and perhaps caused by) insufficient warm up. Massage doesn't help much with inflammed bursa, other than relieving some of the pressure caused by muscle tightness.
As far as other muscle issues, you want to be looking also for the triggerpoint in the supraspinatus attachment just below the acromion, and the triangle pattern of triggerpoints in infraspinatus. I have an instructor who says that shoulder conditions will not be resolved without working teres minor. I've found that to be true. Since all of these muscles are easily accessible, I would imagine you have been working on them. If he were my client, I'd also be checking out serratus anterior and subscapularis.
Rather than static direct pressure for the triggerpoint work, I'd use the short, (1/2 - 1") pin and stretch work for TPs followed by some gentle facilitated stretching. I also wouldn't dig on the knots till they're gone, just try to get them moving toward resolution, then let the kid's activity (and warm-ups) work the rest out. You can also use the technique where he creates resistance, then you go for the knot while the muscle is contracted. This can be very effective for athletes.
Don't do deep work less than one full day before a game, and he has to take it easy with practice. Fast pitch seems to take significant toll on pitchers, due to the snap at the end. And you don't want the muscles to be already fatigued due to deep tissue work on game day.
Besides ice, warm-up well. Poor warm-up can lead to -itis , (inflammation) rather than -osis (wear and tear) of the rotator cuff tendons, although unresolved inflammation often becomes degeneration.