Question and If Yes Are the Special Teams for the Bengals That Lacking Upstairs?

At the game in cincy this past sunday I noticed steelers rushed 10 on one punt and left both Bengal gunners uncovered.
I'm thinking the gunners are eligible to catch a pass right? can someone who knows the NFL rules well confirm/deny that for me. If I'm correct why in the world did the bengals not audible to a fake punt. Seems like a its a given to do this.
Bengals were not backed up very much about at their own 20. I can't remember the down/distance on that 4th down play. AB had to make fair catch on the punt in anycase cause both gunners ran down field untouched.