The answer is yes and it is often a good technique to do so for reasons other than a spotty key bg.
You could have tried it your self you know. You wont break anything by trying.
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You should - if you didnt' already - consider also using garbage mattes to cut unnecessary material out of your shots. If there are areas of the screen that never come in contact with the foreground/subject, then you can eliminate some of the compositing work by masking those out with the garbage matte. You can also animate the points on the garbage matte as well so that is an additional layer of control when you're trying to reduce the number of color variances on the background/chroma layer.
I tried a 2nd ultra key to take out additional background but it does nothing
never thought of animating points of the garbage matt thanks