Which UDS model do you have? According to the docs, the UDS-10 and subsequent models should use port 9999 for telnet config... maybe a firmware update is available?
As far as dynamic DNS is concerned, I have a no-ip.com address from the dial-up days that reroutes all traffic (including telnet) to the domain so that telnet://luddite.no-ip.com hits my BBS just like telnet://ld8.org , so you should be okay going that route. Assuming the network isn't completely bolted down, couldn't you just have the UDS connect on a non-standard port? Presumably your BBS doesn't care much how the UDS is set up so long as it delivers a serial connection.
As far as dynamic DNS is concerned, I have a no-ip.com address from the dial-up days that reroutes all traffic (including telnet) to the domain so that telnet://luddite.no-ip.com hits my BBS just like telnet://ld8.org , so you should be okay going that route. Assuming the network isn't completely bolted down, couldn't you just have the UDS connect on a non-standard port? Presumably your BBS doesn't care much how the UDS is set up so long as it delivers a serial connection.