Change the last line to:
Code:
/run SendChatMessage("Aethran cast Raise Ally on "..UnitName("mouseover")..".", IsInGroup(LE_PARTY_CATEGORY_INSTANCE) and "INSTANCE_CHAT" or IsInRaid() and "RAID" or IsInGroup() and "PARTY" or "SAY")
Uses IsInRaid/IsInGroup, but also supports the INSTANCE_CHAT channel added in 5.1 for LFG/LFR/battleground groups.