I think it's ok to bite a style as long as you are doing it for a line/verse/song and you are trying to pay homage or make a point. What's not ok is style stealing:
The Realest - bit 2pac hard, voice, style, content, adlibs, etc.. Obviously, The Row gave him his marching orders. Who knows? The plan might have been to create more "unreleased" pac content.
Topp Dogg - Same as the realest except he was The Row's Snoop Dogg. shameful
The Game - When he first came out he was rapping with B.I.G./ Shyne voice.!!!
Shyne - Puffy's B.I.G. replacement.
Dana Dane. How did this guy get a pass for biting Slick Rick's accent?