As Salamu Alekum dear brother Salem,
Um, I think we are not allowed - as practicing muslims - to judge others' faith, nor to call them whatsoever without prove, for this's for sure with Allah is a great sin
Let me brother, with due respect, remind you of the following verse and Hadith:
{O you who believe! Let not a group scoff at another group, it may be that the latter are better than the former...} and {O you who believe! Avoid much suspicion, indeed some suspicions are sins. And spy not, neither backbite one another. Would one of you like to eat the flesh of his dead brother? You would hate it (so hate backbiting) . And fear Allâh. Verily, Allâh is the One Who forgives and accepts repentance, Most Merciful} (49: 11-12)
"There's enough ithm (sin) for anyone just to talk all what he hears كفى بالمرء إثماً أن يحدث بكل ما يسمع"
So who knows, may he (samy yousef) be even better at Allah than myself, althogh I don't listen to music, can't it be? actually it's one of the fundamentals and wonderful basis of Islam; NEVER TO LOOK DOWN ON ANY PERSON, for I can never know, may be this person is better than me, and I'D RATHER TAKE CARE OF MY OWN SINS AND FAULTS, for that what I'll be asked upon on the judgement day...
Yet, and to make things clear; only knowledgeable scholars have the right to warn against some specific person, if he's doing something that's completely wrong, clear and against Aqeda (faith) that may affect faith of others to beware of him, and this should be done in an honorable way, suiting the morals of Islam..
Regarding Samy Yousef himself, I'm with you that he shouldn't have used music in his nasheeds for the music is forbidden, may Allah forgive him for this and guide his heart, but brother for whomever'd like to listen to him, there'r always another version with no music (just percusion). On the other hand, and I don't believe he's Sufi, no evidence on this, not even the way he's singing his nasheed (ya mustafa), as it's an accepted way in arabic, besides, if he were sufi, I guess we'd have know it, such thing can't be hidden for long
I'm sorry brother if I offended you in any way, please forgive me for it
Wasalamu Alekum Warhmato Allah