Yes and no.
There are two things.
There are cards and there are Pokemon once they are in play.
As a card, a Level Up card is just that, a Level Up card. It's a Pokemon card, but not a Basic Pokemon card, nor an evolution card. It is a Level Up Pokemon card.
As a Pokemon in play, it is the same stage and evolution state as the card it leveled up from.
So, if it leveled up from an unevolved Pokemon, it remains an unevolved Pokemon.