I just double checked this installer and it worked fine for me. By default it installs the VST plug-in to the c:Program FilesCommon FilesSteinbergVST2 directory, though can you change this when you run the installer. Can you navigate to this directory and confirm that the VST plug-in is located there? It should be called UltraChannel.dll.
If it is, it's likely that this is not the location that Studio One is looking for your VST. You may have to check where Studio One is looking for VST plug-ins, then run the UltraChannel installer again, and install it there.