Are baby livebearers safe from common plecos, clown loaches, or cories?

Only clowns may cause some concern, IMO. Aside from the parents, of course, who are very well known for this behavior.

I wouldnt leave the pleco or cories out of the picture. If they can catch a fry, then they will eat it.

isolate them somewhere if you wan't to keep them around. breeders net or other tank preferably.

My cories love baby guppies. I do not try and save many as a rule and they are a great source of live food for other fishes. At one time i did raise them and found Lee's double breeder a great asset. You can isolate the female when she is with in a week or so of giving birth and there is a grate near the bottom that the young fall through so she cant eat them. You can leave them in there until they get some size as to be safe from being eaten.

If you want to keep them, you will have to move them to a small grow-out tank till they're large enough. I haven't seen my bristlenose go after those little guys, but for the clowns it'll be "snack-time" !

My experience with swordtail fry and my common pl*co has been a good one. Ralph (pl*co) hangs out with fry in his cave. I think it would depend on the individual pl*co's personality. Mine is gentle, shy, and deformed.