There are strict limits about how much you can donate to a campaign, and it's not that much. You can give $5k to their PAC and another $6,600 to them. (That's theoretically $3,300 for the primary and $3,300 for the election.)

The candidate can give their own money to the election, but they can't be used to filter donations.

You can give as much as you want to a SuperPAC, but the SuperPAC can't be connected to the campaign. They give an awful lot of leeway in the interpretation of "not connected", but having the VP candidate request it might be too much for the FEC.

Still, Thiel might be able to promote Trump. But he can't "bankroll" the campaign.