Can I use ground leg of lamb for Lamb Merguez?

I agree with MrsWheelbarrow unless you have a leg with a fair amount of fat. I do grind my own sausage meat. You could use shank too.

Leg of lamb is a little lean for the sausage. Shoulder is the best cut (or neck, actually!) If you are not grinding it yourself, ask the butcher to grind up lamb stew meat.