Good Afternoon,

I don't see anything "wrong" with using plastic reels in a SS tank, but generally the plastic reels are larger in diameter and won't fit into the standard 35mm/120 SS tanks.
I just dug out my old Patterson reels, which I haven't used in at least thirty years, to confirm this. The Pattersons will, however, fit easily into a larger diameter Nikor tank made for 220 metal reels.

I see no point in the plastic reel/SS tank combo. SS reels are significantly easier to load, require smaller amounts of chemicals, and are dead simple to keep clean. In addition, I also recall that, in some of my early attempts at developing, I had problems with uneven development near the edges of 120 film in plastic reels.