Honestly, in a 4-man group running an instance normally you should never expect the bard to give you mana. On the other hand if you are doing something such as WP speed runs or generally doing 2-3 group pulls (or more) where massive aoe's are needed, then yes it can be expected as you will need the mp to keep hate.

I do not know all of the tank taunts and skills n such but in general as i understand. Tanks should use flash (aoe taunt?) then tab and individually taunt mobs with emphasis on whichever is marked 1 or to be killed first. This keeps mana usage low but hate yield high.

With well geared and under geared tanks alike, in normal runs i have never been asked for mp nor do i believe i should have to give mp for general pulling. On the other hand when it is absolutely needed I will put it up. But realize that using an mp song lowers a bards dps by 20% thus making most reluctant to use it.