Basically, yes. It would appear that the plasma explosions are not
exotic damage. Also, based on what I gathered (someone please feel free to correct me if I'm wrong) The Bio-Molecular Torpedo and Withering Disruptor procs are also not
applied as exotic damage but rather as Radiation Damage. Skills/traits that improve exotic damage such as Starship Particle Generators and Particle Manipulator won't affect these weapons since they offer no exotic damage.
If you're interested, you may want to try the Particle Emission Plasma (PEP) Torpedo from R&D. It creates a plasma cloud after impact which is
treated as exotic damage and boosted by all relevant exotic damage-boosting skills.
I checked on Sto Wiki for both the PEP Torpedo
, Withering Disruptor Beam Array
, and Bio-Molecular Photon Torpedo
and checked the skills which affect the weapons. Sure enough, the PEP torpedo listed Starship Particle Generators, but the other two weapons did not. From this I came to the conclusion the Withering Disruptors and Bio-Torpedos do not
offer any exotic damage.
I think that just about covers it. Please, someone correct me if I missed anything, sometimes the wiki can be outdated.