Any agent regardless of their specialty will have had combat training, I get your point, but you are making it sound like they are sending out the lambs to slaughter which isn't the case. I'm a former US Marine and all Marines are rifleman first and foremost regardless of MOS, at anytime a Marine can be rotated into a combat element even if he was a cook,paralegal etc. They might not have as much experience as those of us with combat designations but they have the training and have seen guys like this excel and survive in combat.
The Sith probably did send the agents in hoping some would get slaughtered but knowing the Sith philosophy I think it was less about wiping them out and more about culling the weak from the strong for when the new Intelligence is rebuilt.
Comparing marines to surveillance agents and spies is inappropriate. Marines are a combat unit (as you stated yourself, riflemen first and foremost) while Imperial Intelligence is primary a surveillance and espionage organization.
Edit: Replaced the "absurd" with the "inappropriate" for the sake of nicer discussion.