Well, not during exposure, but you must have the enlarger on to align the easel to the image. Especially if you are cropping in the easel, this can be quite a fiddly process. I usually put a blank sheet of paper in the easel for focusing and alignment, but with the safelights off with the enlarger on it's hard to see the black blades of my easel. I usually end up turning the enlarger on and off rapidly using the persistence of vision so I can see the easel and images alternately but it makes more sense to me to just leave the safelight on. My exposures are usually less than 30 seconds and the paper is in the developer tray under safelight longer than that, so I don't see the point.

I have a homemade enlarging meter but since I calibrate it every time it would seem that the safelight wouldn't effect it any.