They will certainly help you show off your gains, though I'm not sure if they actually affect gains directly. Kegels will improve your erection strength which will in turn show off your maximum length and girth. For myself, when I have a slightly less than 100% erection, my length especially suffers. At 95% erect, I'll only measure about 7 1/2 or 7 3/4", whereas I need a full 100% to measure out my current length of 8 1/4". Girth suffers too, but not as much.
I've done a kegel routine for about half my Penis Enlargement career, and I cannot vouch that they've helped nor hurt my gains. The first 1/2" I gained I was doing a 10-20 min. kegel routine everyday, whereas I was doing no kegels at all during my past 3/4" gain.
If kegels and PC function could affect anything, I'd guess they would mostly affect girth gains. I use kegels to force extra blood into my dick for uli's, [words=http://www.mattersofsize.com/forum/penis-enlargement-forum/12539-slow-squash-jelq-nothing-give-me-better-expansion.html]
ssj[/words]'s, and simple jelqs. A strong PC from a kegel routine will let you get the most out of your girth routine. Many other users on here will sing the praises, including DLD who sees kegels as a major contributor to his legendary gains.