By bestowing recognition (and implicit approval) on a sinful relationship? How could that possibly be construed as "sharing the Gospel"?
Accessory to Another’s Sin
I. By counsel II. By command III. By consent IV. By provocation V. By praise or flattery VI. By concealment VII. By partaking VIII. By silence IX. By defense of the ill done
That would of course be wrong. But the article --- brief and ambiguous as it is --- doesn't say they are bestowing approval on the relationship.
It would be like welcoming a divorced/remarried son and his "new" wife, when his first wife is still living. He is, as Jesus Christ Himself said, living in adultery. But that doesn't mean that he and the second woman are not to come to your house.
That's a tough one.