All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If this beggar is needy or that the Imaam does not know his condition, then it is permissible for the Imaam to allow him to beg people for money. However, if the Imaam knows his real condition that he has no need to beg, then he should stop him from doing so as a way of forbidding evil. It is confirmed that the Prophet said: “Whoever amongst you sees an evil, he must change it with his hand (physically); if he is unable to do so, then with his tongue (speak out); and if he is unable to do so, then (he should detest it) with his heart; and this is the weakest form of Faith." [Muslim]
Allaah Knows best.