20FPS = 20 frames per second. At that rate, each frame is displayed for 1/20 of a second, or 50ms.
If, when playing back, the FPS that is displayed is less than 20 frames per second, and you intend to play them back using the conductor, then some of the effects on the PC monitor will not show correctly. Say it's telling you the playback on the virtualizer is 7FPS, that means the screen is refreshed every 1/7 of a second, or every 142ms (and change). Too slow for catching all your effects.
The conductor is outputting at a set rate, no matter what, all nodes will receive a command 20 times per second, every 50ms.
When, and if your sequencing ask for effects that are changing faster than every 50ms (say by computing a transition or a macro, and having the settings set so as the intervals generated are smaller than 50ms), it's a grey area as to what will be used on the conductor. Could be a blend of all the colors during that 50ms 'conductor interval', could be last one in that interval, could be first one…
As far as shimmer is concerned and it's result with the conductor, I cannot tell you if it works 100% great as I am not using it. But I am using twinkle, which is similar and I have seen some issues when exported to the conductor. It does work with some colors but not with others. Well I am not 100% sure that it has anything to do with color per say, but I have a 20 seconds section on one of my sequence where one of the element goes through 10 different colors, blending from one to the other, using the twinkle effect. When played using the LSP scheduler, it works. When played using the conductor, just a few of the colors (sections) are actually twinkling. The ones not twinkling are just being displayed as if I had used the ON effect.