Hi,
Remote Management can be enabled from a LAN client to a DirectAccess client connected on Internet. It just requires IPv6 end to end connectivity. With UAG, your client just need to be an ISATAP client of the ISATAP router (UAG Lan interface). It's possible but complex. I developped another solution based on DirectAccess client requesting assistance from another DirectAccess client when both are located on Internet. Have a look at it and tell me if it can fit to your need. I will adapte it to UAG :