Hoover was elected on the promise to protect small farmers against foreign competition. You're not going to get him to veto. His exact words were, 'Promises made, promises kept'. What principle, but unfortunately he took a principled stand on the wrong issue.
I'm actually just starting into a book by Thomas Rustici about the economic, and especially monetary, effects of the tariff. In a word, you're absolutely correct in that the Smoot-Hawley Tariff was the immediate cause of the Depression and, probably, the stock market crash. The way to avoid the tariff is to have it become dead-in-the-water in the Senate. There was a group of Senators who absolutely supported free trade and opposed tariffs in the 71st Senate. Their collective decision to give up their opposition in return for protection of their states' major products was what made the difference between the tariff bill being successful or not.
Coincidentally, this occurred on October 21st, 1929. Declines in the stock market began the next day, as the more astute traders noticed the brick wall their national train was heading towards and wisely decided to jump ship. Things culminated in the total crash on October 29th.
We need to try and find out who the Senators in question were, which probably involves me digging through my book. I'll work on it.
Once we know who they are, we need to find a way to get them to not doubt the truth of their convictions. If any increase of tariff rates can be forestalled, than the Great Depression is averted and the US experiences a minor recession in 1929 and early 1930, which it recovers from and which leads to a 'Roaring 30s' scenario. A few tail problems include the on-going agricultural depression, which lasted throughout the 20's and is likely to continue into the 30's. Likewise, Europe is going to have a tougher time of it than the US: Germany has been in recession since 1928 and will probably continue to be choleric through the early 30's.
Additionally, most of the world has jumped on the interwar gold exchange standard, so there's going to be some inherent instability until a more proper coin or bullion standard can be re-implemented. I imagine the 30's will be somewhat more stable than the 20's, but not completely so. Look forward to minor recessions every few years and a major one every decade or so until something better than a gold standard can be implemented.