What does help keep scar tissue from building up in shoulder after a rotator cuff surgery?

Nothing: After rotator cuff repair, you want some degree of scarring to occur as this is how the tendon heals itself to the bone. The problem is sometimes, some people heal too much and become very tight after surgery. Majority of patients will gradually "soften" over time. Early motion while debatable in my practice is avoided as it has been shown to increase odds of failure (cuff et al). Good luck.