I cant really tell by that pic, but it looks like the mag doesnt have the little lip on it to act as the feed ramp (since the saiga doesnt have a feedramp built in to it). Also the little mag-catch lip looks too thick.
All in all, the vepr mag looks just like any regualr ak mag meaning that you would still need to do the same modifications (install a feed ramp, grind the mag catch) to get it to function properly in your saiga.