[quote=@Zeal]
<Snipped quote by souleaterfan320>

Spirit and Lunar would just die and reincarnate to life over and over. 
[/quote]

Basically the same with Alucard.

If you read up on the Hellsing ultimate Wiki, it states that after he consumed Schrödinger, he gained the ability to be 'everywhere and nowhere'. Basically the closest thing to a true immortal.