Allow me to break up your question into 2 parts:
If so, do I need to purchase a separate runt time license just for the test server?
- Do I need to install the run time version on the test server in order to be able to load test that server?
No. The load test will run on a local machine generating large volumes of traffic and sending it to the remote server. Nothing needs to be installed on the remote server to run the load test and get basic measurements such as average response time, request/second and so on. We have a lot of metrics that can be measured by the sending machine.
- Do I need to install the run time version on the test server in order to be able to gather metrics from that server?
If the metrics you are after are part of the Windows Performance Counters, then yes. This includes things like memory use, CPU use, SQL server use and so on.
For question 2 above, yes that is correct.
However you do have one other option to consider. You do have 2 licenses of Test Studio Ultimate. The ultimate edition includes the features, just like the runtime edition, for allowing the load test machine to pull the Windows Performance counters from it. Thus you could run Ultimate from one machine to run the load test and install your 2nd license of Ultimate on the server just for the purpose of gathering performance counters. In the long run this is the more expensive route to take as you're consuming one full license on a server only for the purpose of gathering performance counters. But in the short term it allows you to get the counters w/o any additional purchases.