Hey Great questions.
You can definitely use manual rotator for mosaics. And the mosaic does not have to be a mosaic it can be a single frame.
When you use the framing / mosaic wizard you can frame out even individual frames. I use the wizard for all of my images because it takes the guess work of how the image will be framed.
You first need to have plate solving working before attempting to use the framing wizard, so get that going first.
When you use the framing wizard after you draw your frame either a single 1x1 or a mosaic AxB size (based on your camera sensor settings) it will create a target for you in the sequencer.
When you start the sequence SGP will plate solve its way to the target and slew your mount. when it centers it it will then check the rotation and ask you to turn either X degrees Clockwise or Y degrees counter clockwise. Then it will take another picture check and get you closer. Once you arrive at your threshold (ie: 1-2 degrees) you can then proceed and the images will begin.
To use the manual rotator choose "Manual Rotator" from the rotator drop box otherwise you will not be offered this rotational check during the centering sequence.