Which implies that there is a notion of absolute good and absolute evil, irrespective of cultures, religions and pantheons in the setting. If there is no absolute good and absolute evil, then paladins cannot exist - what *can* exist is Holy Warriors. And I would personally use the template for Priest Semi spell user provided in the Channeling Companion (RMSS/RMFRP).
Not sure I completely get the distinction - IMHO, there doesn't need to be absolute good and evil as long as the paladins _absolutely believe_ that there is universal good and evil. And, as an aside, in many fantasy worlds belief is enough to give birth to an actual deity (or give a new facet to an existing deity) -> we'd get deities representing these strongly believed ideals into the pantheon.
That's relative belief. I don't have a problem with that per se, but I have a problem with that AND paladins.
Paladins are embodiments of a "a specific value of Good", which is both independent from their culture and independent from their religion - they don't *choose* to be Paladins, they are *chosen* to be, and not by their gods. In a less apocalyptic way, they are to Good what Moorcock's Eternal Champion is to Destiny. The only thing is, they can choose to discard the mantle of paladinhood, whereas Elric and the others were pawns until their demise.
IMHO, you might have many different beliefs about what is good and what isn't (that's relative belief), but Paladins are embodiment of an absolute Good that transcends relative belief.
And, incidentally, it heavily restricts them in how they can react to everyday life. They might go against the tenets of their deity to preserve and further absolute Good and still keep full access to their powers (but they earn the deity's wrath...), but if they stray from the path of absolute Good, then they will lose their powers even if they stay faithful to their deity.
And that's why paladins are a conscious setting choice on the GM's part: having paladins means there is an absolute truth, regardless of whether or not the characters know it. If there is no absolute truth, there are no paladins, regardless of what the characters believe. All militant servants of the gods are holy warriors, and they all believe that their faith is right and that they are the good ones and the others are, at best, misguided, and at worst outright evil.
As a matter of fact, Rolemaster, and especially Spell Law, supports both. Such spell lists as Lore (Channeling) include spells that explicitly refer to absolute good and evil. On the other hand, other lists, such as those of the Mythic, explicitly supports relative good and evil, interestingly with a different wording ("enemy"). It is easy to have relative truth in a setting with absolute truth - overarching good and evil, but relative divine powers underneath. On the other hand, it is impossible to have absolute truth in a relative truth setting - if you, as a GM, state that all beliefs are equally valid, then you explicitly stated that one cannot be right and another wrong.
But if, as a GM, you state that the setting is one of relative truth, then you have to curate the lists somehow, because some of them include an explicit reference to absolute truth. And my personal opinion is that, in this case, paladins should be curated as well.
Paladins, in RM as in several other fantasy RPGs, are embodiments of absolute good. They might also serve a deity, but they *do not need to*.