I think the question is could a six-limbed (2 arms, 2 legs, 2 feathered wings) flying humanoid evolve naturally on an Earthlike planet. The answer, I think, is yes*. I don't think the end result would look much like a human though.
Environmentally, I think that you'd probably be looking at a near earth-sized moon orbiting a gas giant, heated by relatively mild tidal forces. Lots of volcanoes, quakes, new landmasses erupting out of the ocean, tsunamis, etc. etc. I would also expect that gravity is a bit weaker, and the atmosphere a bit thicker with a noticeably higher oxygen content. That would mean you've got a little more room to play with in body size, but they wouldn't be able to fly on Earth.
The key is that I would expect six-limbed life to be common in charismatic megafauna. Basically, I'd expect stuff analogous to centaurs, lammasu, sphinxes, and dragons (not large ones, obviously) to be fairly common on that world. The obvious advantage to flight on this world is that it allows them to escape the disasters much easier, and colonize new land masses very quickly.
As I understand it, the main body engineering issue with powered flight is the ratio of surface area to volume/mass to propulsion. To get moving you need propulsion, to stay aloft you need a huge surface area with a narrow profile compared to your volume/mass, but the bigger your surface area, the more mass you have. The more mass you have, the more propulsion you need and the more surface area you need, which costs more mass... and basically the bigger you get, the greater the difficulty in powered flight.
I would expect that each wing is about as long as their body. So if they're about 5 feet tall, I would expect a wingspan of about 10 feet, before any feathers. Feathers would probably add another 2 feet in length on each wing, giving them a functional wing span of 14 feet. I would expect that their manipulating limbs, the ones that look like our arms, to be quite short. I'd guess their fingertips would touch their hip bone. Their resting position for the arms would probably be curled up to their chest, like bird legs. I would also expect that their legs would perform much the same function as a bird's tail, and thus have a rather impressive amount of plumage. Their feet would almost certainly be more like a hawk or an owl's feet, with a larger central "ankle" area and stubbier toes- no talons though. I imagine that they'd stand primarily on their toes. Their face would probably look a lot like a canine's, but with larger eyes, smaller ears, and a much larger brain pan. I'd also imagine that their entire body has some form of feathers covering it.
They'd need a huge heart, massive wing muscles, hollow bones, and very very efficient lungs, even with the higher oxygen percentage in the atmosphere. They'd fly like vultures or geese, which would help them save energy. They'd need to be primarily carnivorous, to fuel their metabolism, but I could also see them going after seeds and other high-calorie forms of sustenance.
I suspect that you'd see a lot of similar adaptations to birds on earth, with their red blood cells having nuclei and able to see into the ultraviolet. Heck, these 'angels' would either be like birds, and lay eggs, or be like marsupials, and have a stretchy pouch for their partially developed babies. I doubt they'd give birth the way a human does.
If they're tool users, I'd imagine nets to be their primary tool for hunting. In the air, I'd expect lances, bolas, or javelins. They may also have something like a knuckle or a spike on their wings, which would allow them to use their enormous wing strength to defend themselves on the ground.
So basically, you'd end up with something more akin to nightmare fuel than angels if you tried to engineer a biologically successful hexapodal flying creature.