Is it advisable to run both Terminal Services (application mode) and SQL Server on the same cluster together?
Technically speaking, what you want to do is possible, but I wouldn’t recommend it. One problem is that Terminal Services (Application Mode) has some limitations under clustering, and is not fully cluster aware.
But the biggest problem you will run into is performance. Terminal Services (Application Mode) is a huge resource hog. The same is true for a very busy SQL Server. If your SQL Server activity is low, and your Terminal Services sessions are few, then they might be able to co-exist together, but I still would shy away from it because of the added complexity of putting both on the same cluster. Clusters still are a little tricky to set up and manage, and adding Terminal Services and SQL Server into the mix at the same time is just asking for trouble.