According to the fallout 4 videogame, yes actually. It is. What you have moved on to is not featured in Fallout 4.
Cait kills raiders in the ring, and that is it as far as participants and spectators go. Tommy is the only non-raider in the room.
If we move outside the game itself, and assume that raiders throw some farmer in the ring because they make him do it or else they kill his family, then I don't know. A raider probably would kill him. Cait would probably kill him if she didn't know. But I could see Cait saying "this is stupid" and not fighting. The reason I believe this is because she has shown that she doesn't like stepping on the "little guy" in things, and when people play with people weaker than them, Cait doesn't like it. Probably because she was a kid when a lot of her bad stuff happened and she can relate.
If the farmer says "yeah, this is dumb" and the raiders shoot them both, they die innocent, and the crime is on the raiders.
If the farmer says "now's my chance" and stabs her, she dies innocent, the raiders are guilty, and the farmer is in between them with some blame.
If the farmer says "now's my chance", and Cait defends herself and kills him, she is innocent, and the raiders are guilty.
The questionable scenario is if the farmer doesn't fight, the raiders say they'll kill them if they don't fight, and Cait does kill him. In that scenario, the raiders are guilty, and Cait has some guilt. Telling someone that they should die if someone threatens to kill them if they don't do something is a hard thing to ask of someone. If someone threatened to kill me if I don't do [thing], then I just say ok and I die. But that's because I choose that course of action. You don't reasonably expect that out of most people.
But notice the trend. In all of these hypotheticals, the raiders are guilty, and the farmer and Cait vary throughout each scenario in being guilty or not.
Even in these hypotheticals, there are details to consider.