If you control one and it blows up right next to the bad guy but your teammate happens to have units there. Will your teammate take damage?
im pretty sure it does, splash damage affects everyone but your own units right?
yup, everyone but yourself... unless you attack yourself

Yes your allies are effected by your spash damage just the same way you can't use Lurkers in a defense where your allies are standing.
Your teammates would definitely take damage, as with splash damage. And if you had your own units there, they would also get blown up because of the type of splash damage similiar to the siege tank on siege mode, but different to the reaver.