Specifically, referring to the Summon Monster V Babau option, this creature has Dispel Magic as an at-will SLA.
Per the text of Dispel Magic: "You can also use a targeted dispel to specifically end one spell affecting the target or one spell affecting an area (such as a wall of fire). You must name the specific spell effect to be targeted in this way. If your caster level check is equal to or higher than the DC of that spell, it ends. No other spells or effects on the target are dispelled if your check is not high enough to end the targeted effect."
Identifying a spell that's already in place, however, requires a DC 20 + spell level Knowledge: Arcana check. Without this check, a creature cannot identify what spell is currently being used.
Let's assume we have a situation where a Wizard is fighting an enemy that casts Invisibility. The Wizard summons a Babau and commands it to dispel the enemy's invisibility. The Babau can see the enemy thanks to its constant See Invisibility effect, but can it legally target the Invisibility spell directly without having sufficient ranks to pass a Knowledge: Arcana check to identify the spell first?
Does the Wizard know that it is an Invisibility spell? If so, could it not tell the babau "Hey, dispel the enemy's Greater Invisibility spell?" That should do it, I reckon.
We can assume that any decent Wizard could have made the DC for Spellcraft to identify a spell as it's being cast, so no trouble there. The question remains as to whether the Babau, since it has no Arcana training, can specifically target a spell effect that it has no knowledge about, simply through the direction of the summoner. Is simply repeating the name of the spell enough?
I'd imagine the party cleric would make a decent substitute for the Babau in this situation as well, since many neglect to put much into Knowledge: Arcana.