certainly makes sense, and if you're going to install one anyway, might a well put in both while you're at it.
I'd install 2 if the RD didn't have an adjuster.
AFAIK, road derailleurs all have an adjuster, so in this case it's not necessary in my opinion. Of course, if I wanted to use an MTB derailleur without adjuster with road brifters that also lack it, then I'd install one for the RD as well.