Newbie here...
...All tung oil isn't tung oil. By that I mean just because it says tung oil on the can, doesn't mean it is tung oil. For example, the MinWax tung oil you get at Home Depot is tung oil mixed with varnish. Nothing wrong with that necessarily, just pointing out that there are lot of products that say they are tung oil, but are something different than what you expect. Various other tung oils may contain blends of other oils and/or varnish. The advantage of the Minwax tung oil over real tung oil is that the Minwax hardens up in a reasonable amount of time. 100% tung oil takes a long, long time. Usually if a product is pure tung oil they will proudly mark that fact on the can. If it is a blend, then you have to play detective and read the ingredients.
The reason why I mention all this is because if someone mentions tung oil, they might be talking about a specific product that may or may not be 100% tung oil, so the question is a little more complicated that it seems at first. I believe that Warmoth doesn't warranty bodies or necks finished with tung oil for this reason, there are simply too many products out there claiming to be tung oil for them to verify each one of them. So they have a blanket no tung oil policy.
Tru-oil is polymerized tung oil. Similar in feel and application, but dries harder and faster.