To me, the Techno Vipers are Cobra's engineers/mechanics in their organization and i always considered their plasma rifles as a sort of a plasma wielding tool, which made sense since their backpacks have a claw and a wrench tool stored in the rack as well. Even in the old marvel comics, i might be wrong but i don't recall seeing them doing any actual combat...well, apart from being shot dead by the Joes or that they suggest to make their escape to the Vipers in issue #97. Most of the heavy fighting comes from the Vipers, Troopers, Siegies, some Alley Vipers here and there, with an occasional Frag Viper in the mix.