First: "Terminal Services Cluster". It is not supported to cluster Terminal Services, at least not in MSCS.
One could say a farm of Terminal Servers is a cluster, but the underlying technology is completetly different.
Second: While it is possible to have two (or more) servers seing the same volumes simultaneously it is not supported in the Windows world. The only native method is to use a mechanism to lock volumes to one host at a time, and this is what is commonly known as a Microsoft cluster.
It's perfectly possible to hook up two servers to one external storage system as you describe, but the two servers would access the same volumes with no notion of the other server. Havoc would ensue.
If you want to use Terminal Services in a high-availibilty configuration with this hardware the closest thing would probably to have an active/standby system, where one server is active, and should it fail the other server is booted from the same volumes.
It will only protect you from failures in the actual server. Should the external storage system fail or you get a logical corruption in the file system you're smoked.
/charles