Sigh, no, it is not hearsay. Hearsay is rumor or something you did not hear or witness first hand.
A subject matter expert, what they are called by the courts, is someone brought in by either the defense or prosecution for their opinion on a matter. To become a subject matter expert, at least in my judicial district, one must demonstrate a higher than average knowledge of the subject than the average person. That being said, it is not a very difficult standard to meet. I am a court recognized SME in gang tattoos. Nothing special about that, I have just studied them more than the average person. That does not make my opinion on a tattoo hearsay, it makes it my opinion. The other side is welcome to call their own SME to refute my testimony.