I'm fairly sure Alucard would win if he went level 0 but dante vs alucard would be an amazing death battle.
Considering dante's weaponry is effective against the unholy and he appears to have more technical skill then alucard, it'd make for an interesting fight, especially given Alucard is a walking castle.
About dante royalguarding superman...No, hell supes is designed to be unbeatable XD.
I had this discussion with a bayo fan who said her suit is meant to be invincible, which i'm not to sure of since she that'd make the game easy as hell for her but lets roll with it for a bit, just because a game says something cannot be beaten or is invulnerable, does'nt mean it can't be beaten in death battle, simply put while we've never see anything in dmc dante can't royalguard does'nt mean there's nothing that he can't royalguard, it's always gonna be impossible to know how much he can take simply because the stats are'nt there and there are no universal stats between characters of different universes, so yeah I think given what we've seen of all of dante's other abilities, it's not plausible that this one skill is so OP that it could block supes.
As for blocking the bayo punch, Honestly there's a million things he could do there, he could slow down time again, he could trickster away, hell if he was hit he'd still have his majiin form as a backup, I think Madame butterfly possibly hits more then the saviour but dante barely seemed to care when he blocked that so what's it like when he's at his full potential.
And yeah Bisons right, the fights are really just for fun, death battle is simply an informed opinion more then anything else but they explain pretty well after the fight why they think which characters would win.