We're currently running SOS Collab Server 1.1 (old, yes I know). Is it possible to access the server with a newer client? Specifically soscmd.exe (Which I belive is SOS3.5ish?)?

We had built a very robust autobuild system with VSS but recently had to move to using SOS and wanted to "port" our build scripts.

SOS Collab 1.1 is the last version of this software, and no further releases are planned.
http://support.sourcegear.com/viewtopic.php?t=2591

There is no command line client for SOS Collab. However, you could use soscmd.exe (the SOS Classic command line client) to get your code for builds. Both SOS Classic and SOS Collab can communicate with the same VSS database.

You'd need to install an SOS Server. Contact our sales department at sgstore@sourcegear.com. If you provide them with your SOS Collab licenses, they'll give you an equal number of SOS Classic licenses.

As long as you're installing an SOS Classic server you may want to consider switching from SOS Collab to SOS 4.1.2 and Dragnet.