Yes, as long as the savings are modest and are from allowances or shares of extra pay. It will, of course, be up to the credit union whether to admit you, but should be OK.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
In addition this may give you access to small short term loans if needed as most IVAs allow up to £500 credit without seeking consent from the supervisor.