I've never used a color densitometer, but unless it has a UV channel I doubt it would work. Wouldn't it read the actual color of the stain? Any regular transmission densitometer will get you close enough, if you use a No. 47 Kodak Wratten filter. Basically, what you're trying to do with the filter is to simulate the pyro-stained neg response to blue light. Of course, this was probably closer back in the graded printing paper days because enlarging light "back in the day" was more blue. My Aristo VC head on my 5x4 enlarger has the V-54 (blue/green) tube so, for me, I figure...close enough. I can interpolate from there.