In response to the posts earlier by Chris L and Zensig...
First, I'd like to say thank you for posting these questions. This helps us provide more examples to the public. And thank you Zensig for providing a quick response to the customer.
I did some more testing and would like to provide some additional information regarding connecting to DFS through Remote File Access.
The domain suffix <contoso.com> must be placed in both the "Domain Suffixes" and "Allow" list under the Remote File Servers tab for this to work.
With ActiveSync, the device can access files within DFS.
example: \contoso.comsharefile.txt
With OWA, it depends on the DFS Share
If one wishes to access DFS pointing to a root drive of a server, one must browse to a specific file within that share.
example: \contoso.comrootfile.txt
If one wishes to access DFS pointing to a folder, then one can browse the top level of the share.
example: \contoso.comshare