Its possible to add it but could cause id errors, My suggestion is to use universal electricity's main power mod as galacticraft and a few other mods in tekkit support it, or use ic2 your choice.
It's got bukkit and forge put together and it loads all the new tekkit mods without error plus allows for bukkit plugins. Send me a pm if you want proof.
you need to put the mods into a prerun server with fml installed on it. My recommendation is MCPc + if its 1.4.7 or 1.5.1 for 1.2.5 and below MCPC might still have downloads for those.