I'm not sure why the exchange consultant would say that. Admittedly it is a tad more work for them to enable the IMAP module in exchange and then permit access to those application servers that need it. I doubt this is considered bad practice as the way to do is still described by Microsoft here:-
http://technet.microsoft.com/en-us/library/bb691401(v=exchg.141).aspx
and they usually comment about methods being replaced or about to be dropped.