Someone found this blog by searching, “does Vargo Hoat know about the Red Wedding”.
At this point in the series, Vargo Hoat is dead. He didn’t make it out of Harrenhal alive. I don’t think he found out about the Red Wedding? He was serving Bolton, and I’m sure he would’ve been interested to know about Bolton achieving power over the North by killing Robb Stark, but Hoat was in a really bad way by that time. He was seriously ill and delirious with fever due to having his ear bitten off. Someone may have tried telling him about the Red Wedding, but I’m not sure he was in any condition to understand what that meant.