While wondering this same question and spending some time trying to find a website which displayed the NFL record for number of appearances in a pro bowl (which wasn't easy), I ran across this forum and then finally found the answer. Merlin Olsen wasn’t the only player to appear in 14 Pro Bowls.
Bruce Matthews tied Merlin Olsen in 2001 with his 14th selection to the Pro Bowl...
And for fun here is what I came across for the other big 3 …
NBA - Kareem Abdul-Jabbar (selected to 19, played in 18)
NHL - Gordie Howe (23) (played a few more in minor leagues)
MLB - Hank Aaron, Willie Mays, Stan Musial (24)