I've seen systems with copper baseboard not heat well when tied into an OWB simply because the baseboard was sized for 180+ degree water. Possible with oil, but difficult with pumping in from the OWB.
Pictures of how its plumbed is critical (as many have mentioned), the point where the hot water from the OWB is put into the system would affect the supply temps to the baseboards. Done wrong it could mix and deliver lower temp water, and barely heat the house (like you're describing).
Pictures of how its plumbed is critical (as many have mentioned), the point where the hot water from the OWB is put into the system would affect the supply temps to the baseboards. Done wrong it could mix and deliver lower temp water, and barely heat the house (like you're describing).