My estimate from a graphic analysis of the headband width compared to the HL50 headlamp head dimension is that the Fenix headband is 1-3/8" wide. I examined the Olight headband in the same manner and it seems to be about 1" wide. It seems like the Olight headband is smaller in width, so it would slip into the wider HL50 slots in the headlamp mount, but I don't know how comfortable and stable that would be with a narrower headband, especially if it is less cushy than the Fenix headband.
Why not use the contact form of each manufacturer and ask for the width and thickness of the headbands? That would give you a more precise idea.
I hope that helped. When you do eventually follow through, let me know if it did through PM.