Ssalarn wrote:
"Grappled: A grappled creature is restrained by a creature, trap, or effect. Grappled creatures cannot move and take a –4 penalty to Dexterity. A grappled creature takes a –2 penalty on all attack rolls and combat maneuver checks, except those made to grapple or escape a grapple. In addition, grappled creatures can take no action that requires two hands to perform. A grappled character who attempts to cast a spell or use a spell-like ability must make a concentration check (DC 10 + grappler's CMB + spell level), or lose the spell. Grappled creatures cannot make attacks of opportunity."
" Like a bard, a dervish dancer’s performance ends immediately if he is killed, paralyzed, stunned, knocked unconscious, or otherwise prevented from taking a free action each round."
So, grappled is not listed as a condition that ends the performance, but Grappled does say that a creature affected by the condition cannot move. I'd probably require them to make the concentration check required for activating a spell-like ability each round that they're grappled as a middle ground resolution, but I'm not 100% sure what the RAW are actually dictating here.
Have to disagree, if you would require a concentration check for that, then you would need them to make one every time they did anything else while maintaining a performance (ie. casting a spell, ranged or melee attack, etc.) No where in the description of the dervish dancer archetype does it say he must move around to dance, so the bolded part doesn't really apply.