Honestly I get kind of a Time Lord vibe from him, like Doctor Who. Normally, events are "fixed points" that he can only observe, but if something supernatural "unmoors" it, like Death attempting to meddle in the timeline, he can intervene and attempt to course correct so long as it's indirect, doesn't do further "damage", and largely restores history to how it's supposed to be. In fact, I would surmise that's actually his greater purpose, though he's likely not aware of it. Whatever his ultimate purpose, he seems to regard himself as a "tourist" who lends a helping hand if he absolutely must.
Curse of Darkness raises a few implications through him though: one is that Hector was originally supposed to be Dracula's vessel in a historical sense. Obviously that was Death's plan all along, but Saint Germaine seems to have come from a timeline where it actually happened, hence he tries to dissuade Hector in all the ways he feels he can and not break his own rules. Listening to his dialog again, it's pretty clear he expects his attempts to change Hector's course to fail -- so either he thinks his rules won't allow him to do enough or this is not the first time he's tried. It's obvious he expects to fail though, given the amount of surprise in his voice and expression when he doesn't.
The other interesting implication is that Death is also apparently meddling in history, as his conversation with Germaine implies a history of moves and countermoves between the two of them against each other. There's history there, for certain. But this trait of his never comes up again, so it's possible that Zead isn't the version of Death who is "native" to the 1400's.
My personal read on this (and bear in mind that I say this without a shred of damn evidence; it just seems to fit the situation and dialog to my eyes) is that Zead is Death at the very end of his own personal timeline, going back to where he views history as having gone "wrong" and trying to fix it, paradoxes be damned.
Just like Skynet sending back Terminators earlier and earlier in its attempts to remove John Connor from the equation, which prompts the Resistance to send protectors back further and further, Death has been sending himself backwards further and further in an attempt to create his ideal version of history wherein Dracula's ultimate defeat is averted. But his meddling also attracts guys like Saint Germaine (it may even be him each time) who seem to invariably screw up Future!Death's machinations, while people in each time period by and large don't seem capable of noticing the battle between these two forces (ironically also fitting into the Doctor Who analogy. Said of the Time War: "Devastating to the higher races, but invisible to those below"), probably mistaking Future!Death for his present day counterpart and altogether failing to notice Saint Germaine because he hasn't needed to involve himself that heavily.
Given, that's just how I've come to see things. It's what makes sense to me: that Death's attempt to change history in 1479 is the last great push to avoid 1999's defeat of Dracula. With Hector's salvation, Dracula is ultimately doomed, and Death finally seems to give up.
No real evidence for any of this, mind, but it's one hell of a story that fits what's described in Curse of Darkness, helped along by the fact that not much is described at all in the first place.
If a 1999 game had ever been made, I'm pretty sure my explanation would have been thoroughly jossed. There's probably already some super obscure comic or light novel that never left Japan that does that anyway -- there always seems to be one doing exactly that.