I would be weary doing deep tissue with someone on warfarin, it does depend on their INR as doctor explained, but deep tissue can very likely cause them bleeding.
Are you asking can you do deep tissue work into an area of extreme bruising? - depends, how old is the bruise?, don't massage over recent bruises incase they are still bleeding and you prevent/prolong this, and why is there extreme bruising? is there a fracture or something more sinister you shouldn't be massaging over.