Can a blood curse be removed by a use of remove curse or greater restoration? I've been looking everywhere, but I can't seem to find an answer. I assume it can be, since it is a curse.
The term "curse" isn't really a defined condition in the rules, so we fall back to a basic English reading of the rules.
The Remove Curse and Greater Restoration spells both state they remove one curse affecting the target.
And the various blood curses of the Blood Hunter are, well, called blood curses, and the 'Amplify' parts of their descriptions tend to say things like "This curse lasts for 1 minute ....".
So although they are basically just magical effects you can impose on a target, they are "flavoured" as curses and as such I see no reason that any other rule specifically relating to curses shouldn't apply.
(I doubt it would have much affect on game balance to allow it either - its not that far away from one caster using Dispel Magic on some other caster's spell)