If I understood haste correctly boss frames are now real unitframes. Thus they should poll events like UNIT_HEALTH/UNIT_POWER on unit basis.
Thus you should be able to do sth like this:
Lua Code:
RegisterUnitEvent("UNIT_HEALTH","boss1","boss2","boss3","boss4","boss5")
RegisterUnitEvent("UNIT_POWER","boss1","boss2","boss3","boss4","boss5")
Either this is not working as intended or sth else is wrong. Either way. The bossframes do not update correctly atm.