Hi, i have checked on last eqemu (EQEmu-0.7.0-843) that Bard's song Chorus of Marr (level 64 song) DOESNT stack with regen hp buffs, for example with Shaman's spell Replenishment (level 61 spell). You can check it on Everquest Caster Realm, it say Chorus of Marr stacks with all buffs from other classes.
http://eq.crgaming.com/spells/spell.asp?Id=2106