The simple answer: Not very likely.
You have to match the patch to the version of the game it was intended for. For example, you can’t apply the Eien no Aselia translation to the original PC game, because it was intended for the PC port of the PS2 version (that comes with Seinarukana). Likewise, if the fan patch was made for a specific update version of the game (e.g., 1.04), you’d have to apply the 1.04 patch to the game before patching the game with the English patch.
In general, just read the readme file that comes with the patch. They generally explain technical details like that. And of course, if you don’t want to get burned, don’t buy a game before the translation patch comes out.
Generally this. There are times though when the way the text data is handled in a game, usually a PC game, wouldn’t matter if it was the same version or not. Most of the time edit conflicts would arise and make it impossible.