By default Abilities can't be increased over +6 from any source. You can stack lots of modifiers apart from Abilities, though. So you can have +6 Ability and -5 DR from specific bonuses and that's functionally a +11 on a roll.
For Faith Healer and Malices, I'm inclined to say yes, with the caveat that Malices generally count as life-threatening/life-changing, and so Breaking is required to treat them. Also Faith Healer may not work on all Malices---it's the GM's call as to whether things like curses and psychological issues fall under the purview of the Specialty.