...Are the low pressure shells, i.e. RST, suitable for use in damascus barrel?...
Well, this topic comes up about every 4 or 5 weeks. If you do a search, you will find a ton of advice. To directly answer your question, maybe. If the gun is in good condition, has been checked by a competent gunsmith who knows how to measure barrel walls and you keep the loads down to a reasonable level for both pressure and recoil, then the gun can be safely fired. The RST ammunition is a fine product. It is safe in any gun that can safely be shot.
Pete