Part of what I was saying earlier is that,,,,,,,, there are in most cases, laws already on the books which would curtail much of the use of mudmotors or even any motor for that matter. If you run your motor thru live vegetation and the prop cuts said vegetation, you would be "cutting live vegetation" and in violation of existing regulations ( at least here in Iowa). (does not matter how quickly the vegetation may or may not grow back.)
If you run your motor in open water, shut it off, then push pole, paddle, row, etc, thru the weeds then you would be fine. It would not surprise me to see officers writing tickets for damage done by motors and/or mudmotors.