That’s what I’ve been doing up to now, but it requires xprop-ing the window and editing the configuraiton for each misbehaving application. Given that other window managers do the right thing on their own, I assume it is possible. This is not a complaint against FVWM, just a basis for my assumption that it should be possible to do this automatically.
I’ve also seen this topic
where using the MwmDecor style could configure FVWM to do the right thing for a window with a similar value for the _MOTIF_WM_HINTS atom, which I believe requests no decorations amongst other things. Unfortunately, this does not seem to be working for me, but I was hoping I was simply missing some other piece of the puzzle.