I was thinking that only Shane could do something that stupid. If Vic had to take out Lem, I think he would have used more discretion about the timing and method. Shane took out Lem on the night everyone on the strike team was trying to shake their IA tails. That cloud of suspicion is like a hurricane now.
Except that, by using a Salvadoran grenade, it might just turn suspicion away from them. Remember the Feds' Crown Victorias that went kaboom at the beginning of the episode?
And I do believe there was a threat (veiled or otherwise) against the Strike Team when they took down the Salvadorans yet again during the cocaine bust. Or, at least the Feds were convinced there would be retaliation.
Again, I don't think Shane is smart enough to come with something like that on his own.