Question: are piccolo and vegeta friends?
Answer: They didn't tolerate each other until the Buu Saga when Majin Vegeta asked Piccolo if he was going to the same place Goku ended up in the other world. Before that, they didn't respect each other (especially in the Saiyan Saga) but they both were on the same page (in the Cell Saga) and had the same goal in mind.