<<Disclaimer:  Verify this information before applying it to your situation.>>

There are several areas of  concern with regard to ice cream.  The primary
one as I understand it is the flavoring and the potential use of grain
alcohol  in the extraction process.(ie: vanilla extract )  It is not enough
to trust labels  you must question the source of the 'colorings and
flavorings you see listed there.   Contact the manufacturers directly for a
list of which ice creams are GF. You may still have a difference of opinion
about the potential of Gluten contamination through the use of grain derived
extracts as some chemists believe they are removed during the extraction
process. A more obvious area of worry would be in the flavors that include
any type of 'caramel' or caramel coloring.  Chocolate would seem to be
a safer choice because it is often produced without the obvious vanilla
extract, however, according to an industry source , chocolate is the perfect
'dumping' ground for other flavors that the company wants to get rid of. Only
by directly contacting the Manufacturer will you learn the answers. Good
 Luck.