what's russian slang for smooth as in smooth operator?

That would strongly depend on the context of the situation. "Smooth operator" doesn't have slang for it at all^ it would be хороший/нормальный оператор.

There is "хорошая/отличная работа!" locution, that literaly translating as "good/excellent job". The same, there is "Всё прошло как по маслу" phraseologism that mean "everything went like clockwork", litearally - "everyting went(hapen) like on butter". There is буз сучка и задоринки phraseologism, theat mean "... of without a hitch".

I remember similar additionals: с точностью до миллиметра (with millimeter precision), точно как в аптеке (exactly like in the pharmacy), тютелька в тютельку (dictionarry say, it mean "on the nose"), (попал) в десятку (dictionary say, that it mean "hit the top ten", but it's in russian mean hitting the 10 of the target - http://images2.travmatik.com/uploads/2009/11/mishe... ). It's only that remember.