Do you mean safe as is possibile breaking/injury issues, or safe as in legally allowed?
1. It is safe as long as you pack the bottles properly (peanuts) and maybe mark it this side up or something like that.
2. I believe it is legal (at least for homebrewers) because you would most likely be sending an active beer (unless you filter) and therefore you have yeast in your bottle. You mark the package as yeast samples and send it on.