Yeah but from what I hear, Alucard is much more prominent and popular. Simon may have been the first but he's barely remembered besides being the first.
Simon is just as, if not more, prominent than Alucard. He has appeared in:
-Castlevania
-Castlevania II
-Haunted Castle
-Super Castlevania IV
-Castlevania Chronicles
-Castlevania Harmony of Dissonance
-Castlevania Portrait of Darkness(as a cameo)
-Castlevania Judgement
-Castlevania Harmony of Despair
-Castlevania Lords of Shadow: Mirror of Fate
Also, Simon has also appeared in alot more crossovers than Alucard, as he appeared in many of the Konami Wai Wai World games, was a secret boss in Contra Hard Corps, fought against the likes of Solid Snake, Optimus Prime, Megatron, Bomberman, etc in DreamMix TV World Fighters, competed against Solid Snake, Pyramid Head and even Frogger in New International Track & Field, and appeared as a playable Bomber character in the newest Super Bomberman R. I believe there was also a Konami skateboarding game that also had Simon as playable.
So Simon is certainly more prominent, if not one of the mascots of Castlevania, than Alucard, especially when it comes to crossovers. Even if he's not so much popular by "today's standards", he's certainly not in Konami's "The Nobodies" books.