Matt H, welcome to the W.E. forum.
In general, yes a gouge on a 1500 grit diamond stone is not good. It’s hard to see what we’re being shown in your close-up magnified photo. Could you send another photo? Just a regular closeup photo with a wider point of view.
A “gouge” by definition, is a low spot that’s created when the flat surface is scooped out. I’d think that if there is nothing raised or rolled up on the surface it’d really be no problem. A flat stone with the little low spot would slide across/over the knife edge as you used your sharpening strokes. It’d be like a “null spot” where there was no action applied to the bevel. As long as it is moved back and forth across the knife edge and not used just in one spot, it should have no affect. As a test, when rubbing the stone across the spine of a beater knife, as long as you can’t hear the stone bumping or clicking as the gouge passes over the steel, I think you’ll be ok.
If there is raised portion or piled up steel as a result of the gouge, you would not want to use that. The best choice then would be to ask W.E. if they would replace it. They are pretty good with their customer service. From my experiences with the forum, I expect they would replace it. If the raised spot was tiny and you could gently scrape or knock it off with a small flat screw driver or something, you may then be ok to use it.
My question though is what action caused the gouge. That would not be something I’d want to do again. The 1500 grit is for the fine finish work after the heavy lifting is already done with several of the coarser grit stones.
BTW, the bottom side of the stone is flat and has no abrasives.