I'm sure others can answer this to more length but the short answer is yes, there is. Only the Viasat modem will work. You can, however, add a router of your own choosing behind the modem to handle your own local network.
No you cannot. The Viasat modem is nothing like a cable modem. Viasat will not give you the sepcs nor the information on why only Viasat modems work but, they have to do things no cable modem will ever be designed to do.