Does a bathroom exhaust fan have to vent to the outside?
Bathroom vent fans must be vented to the out of doors. Venting this fan into the attic is simply asking for problems.  The excessive moisture will cause condensation on the roof members, insulation and eventually cause mold. It is never OK to vent directly into an attic even if the attic itself is vented.

So, the simple correct answer is NO.  Your friends are misinformed.