I wouldn't mind, but I'd certainly find something more mobile like SU-122 or SU-100 being more practical in more situations. A 100mm AT gun would just be another emplacement, and Soviets aren't really a camping/ defensive faction given no forward retreat or bunkers and such.
I think the SU100 would suit them more, make it a late call in, better AT than ISU with no AI, not as good as elefant, again the rest of the doctrine would be gimped.
The BS-3 also doubled as a field gun, like the ZiS. I suppose one way to make it work is to use a small barrage or precision strike ability so it's a bit more versatile and similar to how other Soviet artillery works.
It's still an emplacement though.