there are any pellet stoves that are designed to vent into a chimney. You can drop a liner down the chimney for a pellet stove, but only if it is NOT serving any another applance.
Read the manual from the stove, or call them and ask for their input.
not negative pressure appliances. They have a positive pressure vent system. A chimney for your oil appliance is a negative pressure system. You cannot combine the two. As well NFPA 31 specifically prohibits solid fuel and oil venting into the same flue.