Auras, off the top of my head, don't stack on each other. Some, however, can stack with other abilities, such as the Skirantra's Repair Cloud with Reintegration and their Regeneration Bay.
I do know for a fact that Hoshis cannot stack their Repair Bots on a target five times. However, you can still get 60.0 hull/second repaired if you have a fully upgraded Repair Bay nearby (this can even be 70 for a Kol using Finest Hour).
