I am not an electrician, first off. However, I can see some potential issues with this. I assume you mean you have some UF cable? If so, this is a little more difficult to work with, since it doesn't have paper wrappers on the wires...the jacket is kind of molded to the wires. Also, it's probably a PVC jacket, which means it won't bend as easily as the regular indoor romex-type stuff.
Another issue would be looking to the future. You, or the next homeowner in the house might come across the cable in the future and wonder what a UF cable is doing inside. It could be confusing.
However, I don't think it's unsafe.