Two quick questions:
Can the Sniper brigade use its helos in every combat phase or is there a use restriction like twice per turn,etc?
No limit (which makes them powerful little units).
If the sniper brigade infiltrates behind enemy lines, can it still use its helos if it is located in the same hex as another light infantry unit that infiltrated with it? It would basically trace LOC to that unit.
Technically, yes. Generally speaking, until it's Out of Supply, the helos can be used.