Interesting question. I have found this
"
A specially designed helmet was worn by Hardit over his turban." taken from
http://www.info-sikh.com/FFPage1.html
which has pictures of various Sikh pilots (at least one of which is by a jet age fighter), none of whom seem to be wearing helmets though
But that does not seem to be a complete answer as the text relates to the pre-jet age so I'm not sure