I think it began development as the 32X game, and then the work they accomplished on that was probably ported to the Playstation. The reason I say this is because, according to The Cutting Room Floor Wiki, there was the sprite of the Pork Chop from the Classicvanias found on the disc. Obviously an unused pickup, it was most likely a leftover from the 32X Castlevania, as it seems that game would have played more akin to the Classicvanias. But now we're heading into speculation territory.
Speaking of Rondo of Blood, I was at a gaming event this last weekend (The Midwest Gaming Classic, to be exact), and I saw a PC-Engine playing Rondo of Blood. From the little I played of it (the game was on Stage 4), it definitely is a LOT better than Dracula X, with the smoother whip controls and the MUCH faster gameplay.