Well, in my experience he is relatively unknown amongst Dutch metal fans even, so I doubt many people not into this type of music even know or recall him. Hell, I even know a guy who was into Stream of Passion and had no clue about Ayreon. DWDD frequently has niche artists from all kinds of genres (usually not prog/metal though). It is one of the reasons I enjoy that program so much, because there are frequently some surprising bits of non-mainstream art. While it probably helped get him some publicity back then, I don't think it is an indication of how well he is known.
He has a loyal fanbase for sure, but in my experience even within the metal/rock circles he isn't that well known (that said, I don't know many people into prog, prog rock/metal lovers probably know him). But this is obviously anecdotal and not based on any real statistics. I do think recently he has gained some extra traction amongst younger listeners though. In a time with social media, having a shitton of different artists on your albums and have them share it/hype it works really well.