TBH I doubt very much its anything to do with his nappies.
Research suggests that it's actually the very thin disposable nappies that's causing a lot of hip/walking problems in babies nowadays, not cloth. In several countries (Australia is one I'm sure) the dr's/HV's actually recommend and perscribed cloth nappies, good old fashioned bulky terries to help correct clicky hips.
The fabric between babies legs helps hold the hips in place, whereas with the paper thin disposables the legs fall inwards, together and put inward pressure on the hips. If your lo has a little bit of a hip problem the cloth, if anything, will probably be helping him not hindering him.
Get him checked out if you're worried but most babies, even those who walk early, can take months before they're properly steady on their feet as they're still learning and adjusting