hug sb in one's arm正确吗

不对，应该是hug sb by the arm，因为这是一个固定搭配，动词+介词+the +人体部位。中文意思是，拥抱某人的手臂

同类例句

The officer grabbed him by the arm.

警察抓住了他的手臂。

He seized her by the arm.

他抓住她的胳膊。

She was led by the arm to a small room at the far end of the corridor

她被拉着胳膊带到走廊另一头的一个小房间里。