I believe your question begins with a false premise, that using treated wood has some advantage and one possible negative on a boat trailer.
It is true that that wood treatments will interact badly with some metals.
But also consider, there is not much wood on a boat trailer. Any untreated wood on your boat trailer is going to have several years of useful life. There are also rubber parts with a similar life span, not to mention oxidization to the metal.
Your trailer is going to need maintenance. Replacing untreated wood as it ages, is probably one of the least expensive and time consuming maintenance tasks, you will have. Adding treated wood, is going to increase risk to more expensive and difficult to address issues.
Also consider, how much of the time that wood will actually be exposed to the weather, for the longest times of the worst weather, there is going to be a boat over the top protecting the wood and the trailer.