I encountered the enemy team using this to their advantage last night in Blackreach. We were camping their bodies, interrupting anyone who came out of stealth to resurrect their allies... but then one of them started resurrecting from the second level above, through the ceiling. There was no way any of us could interrupt them in time, and thus they were able to resurrect their ally and they both went into stealth.

Resurrection needs to follow line of sight rules, just as every attack against an enemy player or monster does. I don't think this will cause issues in PvE, but if it becomes a problem, then just only enable line of sight resurrection while Battle Spirit is active.