Last time I checked,American built/designed weapons can't be sold by one nation to another without Washington's consent.So you would have to assume that the US govt was also part of this deal as Spain would need to depend on the US for tech support & spares.Afterall,it is also part of the JSF & has built Aegis equipped ships.
I'm certain that the sale was OKed by the Pentagon. Foreign military sales always come with transfer restrictions. The Patriots have limited ballistic missile defense capability against "Scud like" and cruise missile threats. They are nearly worthless agains ICBM's.
It would be next to impossible for Spain to maintain the system in good condition without technical and material assistance from the U.S., in any event.