I've kept juvenile angels with a school of cardinals, and one odd loner neon (outlived his buddies). They are fast enough to get away from the angels, and with a group of angels to bicker among they pretty much ignored the tetras. I would say it should (but YMMV!) be safe, especially in a well planted tank. My tetras were often schooling around in a lower level than most -- maybe to give the angels plenty of room.
And the angels went into the tank with them afterwards and were small to start with. Might help.
Also, if you feed them well, they won't be as inclined to look around the tank for other food sources. (like small fish!)
In my personal experience, angels do well with botia species. They will stand up for themselves, but can't do much damage to the loaches--loaches are fast and usually engaged in observing the fish around them. I've had them with clowns, yoyos, and even modestas and saw no interspecies aggression issues that led to damage. They all seem to get the territory concept and are aware enough of each other's space to cohabitate with minimal interaction. Once the angels got large, they went where they wanted and even would push into a botia-war over algae wafers with impunity. The botia would look shocked, think about shoving the angel, then think again when they saw that evil red eye turn their way. . .
I've had them with cories, too, but cories are so self absorbed that if they piss off an angel they don't even know it and end up getting rammed. Doesn't seem to do any damage, but the cories freak out...and they never seem to figure out what they should avoid doing and it happens all over again. They are not territorial at all and seem unable to grasp the concept that there are areas that they should stay out of...
In your planning be sure to leave a few open water areas for the angels. They'll need about 8" or more of plant-free depth in places where they can just 'hang'. They take up more space vertically than horizontally and especially if you go for the veil or super-veil variety.
When you're shopping for angels look for the following:
Nice round body shape (a slight notch just before the mouth is sometimes indicative of wild blood-not bad, just be aware)
No odd curvatures or indents in the body edges
Make sure they have all their fins! (some inbred strains of angels will be born missing ventral fins especially the light varieties)
Fins wide spread, no splits, planking, or fin rot
Eyes that fit the head, not larger than normal
Active behavior, good color, no dull patchy spots--healthy angels that have been tank bred will automatically come to the front of the tank if they see a person. They will frequently follow your finger if you trace it along the tank.
Avoid fish that hang back, or seem uninterested or are being heavily picked on by the other fish.
Generally speaking, even as juveniles of dime size, males are often larger than females. If you pick a batch that are all the biggest ones, you may end up with mostly males. If you want females, include some mid-size fish too. Avoid the tiniest ones, unless they have many excellent qualities and you think they may just not be getting their share of the food.
Most of the time a tank full of the same kind of angels are from the same spawn, or the same line of parents. Might be a good idea to get some from different tanks to avoid further in-breeding.
The double dark black variety are very pretty, but fragile and sometimes fail to thrive. Likewise the albinos (light gold to white with red eyes).
