Can Rogaine help bring back hair to scar tissue?

No, Rogaine simply sends a signal to hairs to grow if these hairs are in the right condition to grow. Scars don't really provide that right condition for hair growth mostly because the hairs end up being destroyed by the scar, blood supply can be poor and the reserve of hair follicle stems cells is diminished. But in a newly forming scar, use of Rogaine might make sense to facilitate growth and survival of hairs that might otherwise die.

No.  Rogaine acts on hair follicles but can't create them.  Hair can be transplanted into scar tissue.

In general Rogaine simply causes already existing hair to grow thicker/faster. So in areas like scars, it will not cause hair to spontaneously start growing (on occasion it will cause recently lost hair via balding to come back but that's really it). To get hair in those areas you would need a hair transplant, and an in person consultation to see if you are a candidate for one. There are also other options to camouflage it a bit better too, such as SMP.