100%? Probably not. I mean, I'm sure the guy has some assets besides Exxon Mobil stock. Like a house or two, some nice cars, maybe he bets on penny stocks in his free time - who knows? It's not like I have access to his tax returns. Most places list his overall net worth at $150+ million so I'm pretty sure the vast majority of his wealth is currently tied up with Exxon Mobil.
I doubt it is a majority at the moment. He's no fool and not-fools diversify. Sure, he has a large chunk--much more than any randomly-selected investor--in Exxon. But I also have a relatively large chunk in my own company's stock, as they match my 401k with company stock (really, a company stock index fund).
OTOH, he has options that mature in the future. THESE may very well, when they come to fruition, then compose the majority of his accumulated wealth.
It is something to think about, but I would not let the existence of such option or investments keep me from supporting him, were I to support him. Folk who are successful at that level of business accumulate wealth of some sort.
And Trump is even less a worry, since his assets are more real (real estate) and diversified. Trump truly would benefit from general and overall growth in America's economy.