Just wanted to follow up as I was able to get command acknowledgement working by enabling the BK parameter to "on" as stated in the Ultrix manual. I sent:
01 52 30 42 4B 09 45 09 4f 4e 46 44 04
and get responses for every accepted command now. When you connect to the Ultrix, you must establish this as it defaults to off.
#Ultrix