Can, but shouldn't. Need on mp5 item as a mage in rdf, is in short, dps needing on heal item. And you know you roll for the spec you join in as in RDF, otherwise it's a ninja.
"Definitely ninja", mot really. It depends on item rolled and what the mage, and the priest, have equipped.
Yes, there are dps classes that gets SMALL gains from spirit, doesn't mean they should roll for any item that is higher gs and has spirit on it.
Fire mages loves spirit+crit items. Beyond fire mages there are no other caster DPS BiS items with spirit.
Slight exception being alternative demo BiS that focuses on getting SP (via SP+spirit items) to buff raid, last one of those I saw was early/mid 2015. If this is even a thing anymore.
A point though. Some "non-HC BiS items" or "BiS if HC" as some people call them, aren't always better than their EoF variants.