Given your configuration, I am not aware of any settings in ALM that will keep screensavers or the machine from being locked. There are settings that create a longer period of inactivity before the ALM client is disconnected, but none that address the screensaver. As long as the ''automatic runner'' is open in the ALM client, the ALM server will not terminate the connection because it knows you are running a test suite, but that is not to say that the machine may not get locked or the screensaver turned on by some kind of windows policy which could also halt the execution.
The big problem when running UFT tests is that UFT requires an ''Interactive session'' in order for the automation to function, so the best way to think about this is that uft requires a screen to be open somewhere where a user can see what is happening inside that machine. If it is locked or has a screensaver up it won't be able to run the automation.
The most common solution that most users that have this kind of policy enabled is using a key press program that keeps the machine active during the run or before the run so that the machine does not sleep, activate the screensaver, etc. Most commonly the app used is called caffeine and you can get it here: http://www.zhornsoftware.co.uk/caffeine/ this program could be incorporated into the UFT script, you could start it at the beginning of the test suite and then stop it when you are done, you could even start the keypress program through UFT then have uft stop it when you are done. You could also create two ''vapi-xp'' scripts or UFT scripts in the test set, one at the beginning that starts the keypress program and the last set in the test set would turn it off after your tests were run.
I would play around with this and see what works best, I don't believe that you will have much of a problem when actually running the test sets since UFT is going to constantly be acting on the OS which should probably keep the machine from locking or screensaver from starting. I think the bigger issue is going to be the UFT machines becoming locked when no execution is going on, then when you try to run a test on the machine remotely it will not run because UFT requires an interactive session which means the machine cannot be locked.