Acording to what @bley43 stated in post #904579 ,
SNK side:
Iori and Kyo by Shinkiro (obvious)
Kim and Terry by Tonko
King and Vice by Kita Senri
Ryo and May by Eiji Shiroi
He also said that Rugal, Geese and Benimaru by the guy that did artwork for Buriki One (it's Hiroaki but I don't think Benimaru is drawn by him).
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CAPCOM side:
Ryu and Sakura by Kinu Nishimura (obvious)
Chun Li and Cammy (seems to be) by Bengus (don't think so, cause I know that Bengus drawn Vega here, so you can easily compare the style of designs)
Bison and Sagat by Shima Maeda (who da hell is Shim Maeda?)

On the other hand, at http://capcom.wikia.com there's stated that art have combined illustrations of Ikeno Daigo, Dai-Chan, Kinu Nishimura, Edayan, Harumaru and Akiman for CAPCOM chars, & Senri Kita, TONKO, Shiroi Eiji, Hiroaki, and Shinkiro for SNK chars.
So we have no Shima Maeda's (Sagat, Bison & Guile are obviously drawn by Edayan) art here, Akiman drawn Chun Li/Cammy ar by Akiman (seriously), Raiden is by Tonko (similarity in color style with Terry & Kim), Yamazaki by Eiji Shiroi (colors & lines similarity), Yuri is something between Tonko & Kita Senri, Honda by Ikeno Daigo and it's seems like Dhalsim too, Ken is obviously drawn by Dai-chan (his works can be seen in some promotional art for SF EX series). It's also looks like Blanka can be drawn by Nishimura too.