If, by reserve cavalry corps, you mean the regiment/brigade/division/corps structure, then yes, the Allies didn't have Reserve Cavalry Corps in 1805. If we are simply referring to a large body of cavalry as a separate, corps-sized command, then Lichtenstein's Corps at Austerlitz certainly qualifies. But that was my question, what are we talking about here?
As for Murat's massed cavalry at Eylau, I slurred my semantics, I'm afraid. When I said "not all that successful, IIRC", I wasn't referring to Eylau specifically. I was lumping it in with all of comparably-sized charges across the twenty years of war, suggesting that taken as a whole, they weren't all that successful. But, I can see it didn't read like that--at all. ;-7 No, Murat's horse did all they were sent out to do and then some.
It is interesting to note that many of the very large cavalry charges are like Eylau: 'save the army's bacon' kind of charges, where the goal is to delay or disrupt the enemy and shore up weak lines rather than having purely offensive objectives.