Person without tremorsense shoots an arrow at person with tremorsense in a heavily obscured area within tremorsense range? Disadvantage or neutral?
Well, I only pay attention to the sage advice that's in the official document and I don't see a clarification there (and honestly I ignore/override some of those), so I'll give you my ruling.
So let's start with the definition: " tremorsense can detect and pinpoint the origin of vibrations within a specific radius, provided that the monster and the source of the vibrations are in contact with the same ground or substance."
Compare that to truesight: "out to a specific range, see in normal and magical darkness, see invisible creatures and objects"
So I would say the former let's you know the exact location so you don't have to guess where they are, the latter allows you to see them. If you don't have tremorsense you have to guess where something is which may mean that you fire that arrow in the wrong direction and have no chance to hit. So I would say that no, it doesn't change the fact that you are effectively blinded for purposes of advantage/disadvantage.