Is it safe to associate nattokinase with warfarin, under INR control?

Probably not safe. Nattokinase has fibrinolytic activity which is a different mechanism than warfarin which is a vitamin k antagonist interfering with synthesis of prothombin and factor vii. The combination is likely synergistic. The product label clearly states they should not be used together and i don't doubt that the combination would increase the risk of pathological bleeding including intracranial hemorrhage.