Yes, if bleed is a choice in the specials you can add it first and then poison. But poison will remove any other magic ability. If the pet has bleed because of slashing then it will go away, but you can add it back on many pets.
A Cu can get poison and keep bleed.
Im sure lots of pets can get those 2. I have never thought bleed was worth it.
If a lesser has poison as a choice then I will have to make another one. I thought I had all the magics covered. Darn Need more scrolls!!