Hmmm..... I don't know which modem/router you have but I have no problems using NO-IP with Viasat. I have the SurfBeam-2 modem and my router is an ASUS RT-68U. I simply opened port(s) to each device (each device must have it's own open port(s)) and signed up with NO-IP.com. I used ports starting at port 82 and went higher but there are reserved ports in this range (such as port 87) that cannot be used. I would enjoy a faster upload speed but things basically work now with what we get.
I am un-certain about opening ports on the Viasat WiFi modem/router. Someone else will need to advise on using that modem/router combo unit.