Do the PF rules provide any "mechanical" benefits for knowing the "True Name" of powerful creatures (Dragons, Devils, other Outsiders)?
Nope.
It does mean you can use summoning/calling spells to obtain that specific critter, but in Core rules only gives no additional benefit.
Thanks, U.R.
Tome of Magic (3.5) contains rules (and even an entire class) for dealing with True Names. However, I wouldn't recommand this product to anyone, it only brings new, complicated and restrictive mechanics to the table and they are not worthy of the effort required IMHO (even if I really liked Tome of Battle).