Hi heemoth,
Not sure on a definitive answer to this - I always thought that keeping DAB aerials separate is the best idea, plus glass mounted aerials are not always the best...... most experts seem to advise fitting roof mount antenna to ensure the best reception (I assume for this reason).
I found this site pretty good for advice and checking out what aerial solutions are available: http://www.dabonwheels.co.uk/
Hope this helps?