Absolutely not cheating. I believe there is alot of texture to be had by sliding into notes and adding vibrato to them. As far as the slant goes, I would say make sure you have proper intonation on the slant before you slide into it and/or add vibrato. If you are doing the basic slant right with proper intonation, then adding the icing on that cake is good.  But if you are adding the icing before you baked the cake right, "don't do it". Never use a slide and/or vibrato to cover up improper technique.