Harry ji provided the reference with regard to devotional dancing. Itsmaneet ji said dancing is prohibited in Sikhi. One is saying dancing is not useful worship, the other is saying dancing is prohibited in Sikhi, i.e. Sikhs are not allowed to dance in any circumstances.
Gyaniji strikes moi as being the kind of gentleman who might do a little jig if the mood so took him without fear of divine retribution, if I'm not mistaken. cheerleader

cheerleader
Really, applying the same logic as applied to Harry ji's tuk to this one I'm about to post, Sikhs shouldn't be playing tabla and harmonium either!!
ਬਹੁ ਤਾਲ ਪੂਰੇ ਵਾਜੇ ਵਜਾਏ ॥
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/questions-and-answers/38828-dancing-to-kirtan.html
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=38828
Baho ṯāl pūre vāje vajā▫e.
One may beat upon and play all sorts of instruments, ਨਾ ਕੋ ਸੁਣੇ ਨ ਮੰਨਿ ਵਸਾਏ ॥
Nā ko suṇe na man vasā▫e.
but no one will listen, and no one will enshrine it in the mind. ਮਾਇਆ ਕਾਰਣਿ ਪਿੜ ਬੰਧਿ ਨਾਚੈ ਦੂਜੈ ਭਾਇ ਦੁਖੁ ਪਾਵਣਿਆ ॥੬॥
Mā▫i▫ā kāraṇ piṛ banḏẖ nācẖai ḏūjai bẖā▫e ḏukẖ pāvṇi▫ā. ||6||
For the sake of Maya, they set the stage and dance, but they are in love with duality, and they obtain only sorrow. ||6|| Ang 121
It's not about the singing or the instruments or the dancing or any of this outward human STUFF that we do. It's about living a Gursikh lifestyle and focusing on Naam. Dancing can be a wholesome expression, fun, exercise, whatever. (Personally I
never dance, because I have the coordination of a fish in a rowboat.. a la Elaine from Seinfeld...)
I look forward to Itsmaneet ji's clarification.