Can you put DSL on a line that is in a hunt group? Would there be a difference if the phones are analog or digital?

On the phone company's end, I don't think it would matter. Your termination must be analog (POTS). You can have a digital phone system within your business afer that.

If your service is T1, T2 or T3 etc. then No.

Probably a question best put the local telco to see if they provision in that manner and are setup to handle administratively. However, it seems reasonable to me in principle as long as a DSL splitter (not filter) is installed before the analog line is run into PBX.

A Google on the matter yielded conflicting opinions:
Phone System Tech Support: DSL Noise on Phone System (http://www.sundance-communications.com/forum/ultimatebb.php?/ubb/get_topic/f/27/t/000144.html)
DSL Myths! (http://www.nol.net/dsl/dsl_myths.html)

You may have a spare pair from phone system to your jack, add a double jack.