Yes, especially a lowborn. Perhaps a bonus for "knighting" them with their first title, as they go from lowborn to noble. But the again, then perhaps there should be a chance of negative opinion from you current nobility when a lowborn is landed - in medieval society that was not looked well upon and many a king experienced rebellion on that account. In Crusader King it is actually to easy to replace the nobility by appointing new nobles from lowborn ranks.
(...)
I know what you mean (raising someone to nobility), but (in medieval times) you did not need to be noble to be knighted. Lowborn in game might be somewhat ambiguous though, they could be ministeriales and have a low noble background. Even when they didn't, they would belong to the social class just below the nobles.
Actually there were career prospects in conquered and/or colonized areas, the Reconquista, Northern Crusades, Mezzogiorno, England, Ireland and the other various destinations of Norman adventures.
In those cases only the local displaced nobles with a different culture and/or religion may have resented such a move. Replacing nobles with lowborn or lower born favourites within the more established realm would be more difficult, though not impossible , provided it concerned fiefs with had reverted to the crown and weren't taken by force from the previous owner.
However there were some limits in conquered and/or colonized lands too, granting them a county would be possible, but the whole (in game) duchy might still meet a lot of opposition.
Usually a count from an established house was granted a margraviate or duchy, and they usually granted the vassal lords/barons and favourites from their home county, counties, baronies etc. within the new margraviate/duchy.
Perhaps 'resistance' to liege elevating a ''parvenu'' can be scaled, granting a barony to a 'lowborn' should be fine*, but granting that same 'lowborn' a whole duchy should displease established ducal and comital houses (the latter group would have desired to be raised to a duke themselves, and the former would resent having to treat a parvenu as an equal).
(*= they are one step below a landed baron)