The daylight spell says that it doesn't count as sunlight for the purposes of destroying vampires, so it's not like sunlight in that respect.
However, I think I remember reading in Libris Mortis back in 3.5 that the limitation of the daylight spell was due to the fact that there is something supernatural about the sun's rays specifically, which is why even non-light-vulnerable undead try their hardest to avoid sunlight.
However, the daylight spell does temporarily blind creatures such as orcs and drow, so it interacts with living things much the way the sun does in that respect.
So, can a permanent daylight effect act as a "grow lamp" for underground agriculture? If a creature feeds on the plants and fertilizes them with spoor (or previous generations of plants act as mulch), and the cave is extremely damp or has a spring or underground river, can plants live in it? Or does the daylight spell not provide nutrition for mundane plants?
Seeing as how plants can grow with their only light source being horrible, flickering fluorescent lighting in my old office, it seems they're not particularly picky about where they receive their light energy from.