In 1st Edition, Lieutenants could attack twice or move twice, just like heroes. In 2nd edition, the rules do not state if they can or cannot, one way or the other.
The only thing the rules state is they "have attributes and perform attribute tests just like heroes" but nothing else comparable to heroes is listed. It says they are "treated as monster figures for all purposes including figure activations". So I'm assuming they can only have one attack and one move in their turn, unlike the original Descent. But it seems this makes Lieutenants too weak. How can I possibly run that fat goblin Splig with his prisoner if he only gets 3 move a turn? Where are my powerful Lieutenants that can act like heroes??