It may depend on the examiner in your state, but I have never sent one with a trust. Dozens of items have come back approved without a problem. I even contacted the NFA branch about this, and was told that it is not necessary. But, as stated above, its easy enough to fill out and doesn't hurt to include it.
This is just another example of why the NFA process needs to be overhauled. Another question that you will get different answers to, depending on which examiner you speak with.