There should be nothing against it. I have two CB2s with one Zywall110 each in use. One (private) with dynamic IP and Swisscom TV and one (business) with fixed IP without SwisscomTV. The whole thing is also connected via a fixed VPN connection.

Be sure to take the ATP200! The ATP100 doesn't manage 1Gb/s with the UTM services! I'll be switching to a bigger one soon!