I doubt an official answer will be forthcoming, but I believe the answer is no.
Because the GAs are supported by the church, they are not required to pay tithing, at least on that support. I don't know if they are supposed to pay tithing on money from book royalties, corporate board memberships and other internal money laundering, but neither answer would surprise me.
In fairness, if they have outside income, they DO pay on that. But given the crazy things that are permitted as "expenses," it is a sweet tithing-free deal.
They've all had their calling and election made sure, and they've been tithe payers their whole lives, so in a way I think it's likely they don't pay it.
However, what harm would there be in them paying tithing? They get all their money from the church anyway (and more than enough to live on). Like it they get 100,000 a year, maybe instead the church gives them 111,000 a year, then they pay tithing off it (resulting in the same thing, but technically meaning they pay tithing). The same happened with my parents. They used to get money from the church since they were struggling financially, but they would still pay tithing from it.
So, really it could go either way I think. If it's true Mission Presidents don't pay tithing, then it's likely General Authorities don't either.
However, whether they pay tithing or not, it makes no difference. Even if GAs pay 90% of their money in tithing it doesn't change whether the church is true or not.
they dont. they have signed over their possesions over to the church in title only. They are considered like missionaries, MP's: they live of donations that have bene tithed already.
The 15 and the Church are essentially one-and-the-same, so even if they did pay tithing it would be like writing a check out of their own account to pay themselves -- it would be a wash.