They are part of DNSomatic, which the Asus UI supports.
But I too used to use no-ip and they started to send me emails that said not only do I have to continuously use it to keep it alive but also they were picky in which update methods counted as ways to keep it alive (in an effort to get people to subscribe to a paid service). Because of that I switched to an alternate DDNS. However, it might be possible just with DNSomatic.
Seriously if a handful of people contact DNSomatic, they will add new services, if you have one they don't support. I just wrote them a note and asked if they could work with the Asus one (asuscomm.com) because we are entitled to that one for free with our router ownership, but I have more than one thing sometimes I'd like to update w/ my IP (OpenDNS DNS services, a DDNS provider, DSLreports tests, etc.) so it'd be great if they also supported Asus's DDNS inside of DNSomatic.