They may reject them IF they're not on any other eggs. BUT some pairs will gladly accept them. I have a pair that lays infertile eggs and at one point before they laid any eggs I give them a egg to see what they would do, they incubate it immediately. So by the time the pair that had fertile eggs was fixing to hatch, I give it to the foster pair and they accept it and took care of it really good. The pair that I had remove the hatchlings from were horrible parents. This pair raised all their young with flying colors. It really depends on the pair, some will, some won't. I trust this pair because I observed them carefully before I allow it to happen. They've gone through two batches already and did really good.
You really need to understand on how to care for young when they first hatch, it's a hard process!!!! Very tiring....The day they hatch you need to provide some plain yogurt that have live active yogurt cultures in small amount. Then an hour later you need to start feeding the formula by mixing it really watery. You feed in small amounts. Then you repeat the process hourly afterwards, you must make sure the crop is completely emptied every time you feed. So you MUST be committed to do this if you want to proceed, otherwise give it to a breeder who can.