Saviine is a tool to extract from or inject into the console the savegame of your game.
If it's on the console, the disc version use it.
if it's extracted (on computer or SD card) loadiine can use it.
So, saying "saviine can't be used with loadiine" is not really true, saviine has nothing to do with using loadiine or not. But saviine can be used with Loadiine's savegame without problem.
Loadiine save the savegame on SD card.
Saviine can be used to inject a loadiine savegame back into the console.
Of course, if you use the disc or eshop version you need to extract the savegame before modifying it, but if you use loadiine it's ALREADY on your SD card, so you can already modify it without the need to extract it. (no need to use saviine if you use loadiine). It's not that it "doesn't work with loadiine" but more that it's "not needed as it's already extracted".
(disc or eshop) WiiU Internal <-> saviine <-> External (pc or loadiine)