We did this in great detail before, so I'm just gonna say what I said last time.
We've seen Alucard get reduced to little more than a smear of blood on the floor, and he's still been able to regenerate himself fully, in terms of his body and his strength relatively quickly.
The fact is, Alucard can sustain an unending amount of pain, he could be ripped limb from limb, have his body utterly destroyed, and so long as there is still some trace of his being, be it a miniscule amount of blood, he can still regenerate.
Plain and simple, Alucard can not be defeated, he's killed high gods and demons in a matter of minutes, his power is unmatched and that's just in his regular body.
Upon unleashing his darker power to its fullest extent, he can bend, reshape and reform his body, summon familiars to his aid and destroy any being with little more than a vague sweep of the hand.
Dante would be little more than a pest to Alucard, we've seen Dante recover from some damage, but we've also seen him grow tired, worn out and battle weary, the fact is, while Dante may be half demon, he's also half human, and has many human limitations, he's not immortal, and compared to Alucard, his powers are pitiful.
In short, in this match up, Dante gets obliterated.