depends on what you want to achieve. Too vague question 😉
Technically speaking, horizon can work without UAG. But again, your requirements in terms of design and associated functionalities will be the drivers for UAG or not.
I thought that the Connection Server and the UAG could be on one virtual machine. It cannot be, correct? I do not have a UAG at this time and am putting a POC/Pilot environment together. The CS has an external IP and I could deploy a new UAG but was hoping there was a quick option to get the POC delivered. Then I could integrate UAG.
Absolutely not. UAG and CS must be separated they are different OS. UAG is Photon linux and CS is Windows Server.
Also, do never put CS directly Internet facing. It is not secured enough to. UAG is.
for a PoC, as soon as it is internal access only, or eventually if you have another edge secured service like VPN in front of, you can go without UAG, but this is not recommended if you want to demonstrate the performances, especially with SSL VPN and high latency connections.
please refer to the reference architecture for details and Vmware recommendations :