Theoretically, no. But people are whiny, overly sensitive, and oblivious. So if you loot pre-last-1500-enemies in random pub games, you might get accused of general "looting" and kicked from the game. --- Not.
It's not exactly nice to start looting without asking the host/the main builder, since you don't know which items will disappear (Unless you look at each one and determine whether they're over or below the average quality of drops)