No absolutely not needed I have non in my tank!
Also while you see SOME algae in tanks as this is only normal; if you have some type of serious algae outbreak, that means the tank's bio-system would be off balance, so I can only tell you keep the balance between lights, water changes, amount fish (co2) and plants and you won't have issues.
Last but not least also be aware there's many different algae TYPEs that can occur in a tank, any of these so called "cleaner fish" touch one maybe 2 algae types but not all, meaning you could have a total outbreak of 1 type algae and the BN would still not have sufficient algae for him to feed off of.
Why stores always make you want to believe you *need* a certain kinda fish is fully beyond me.
I don't know your stock, but lets say you have 3 Platy and 2 Cory right now, then I'd suggest to up the group sizes to what's more natural to them (in my cases that's ~8fish per group).