Currently yes, Trident under the hood obtains data from the IDL generated by Anchor and it has to have access to the AccountsSnapshots derived for each Instruction Context.
My program Instruction contains custom type such as Struct or Enum on its input, but it does not derive Arbitrary.#
In this case you need to specify same type in the Fuzz Test (with the same fields). And implement From Trait to convert to your type. Check Custom Data Types or Examples of Arbitrary.