I got the same but from Beachwood Canvas. It's welting. I'll wager that it was used between the fenders and cowl only as that may be where the most movement was vs. movement between the fenders and radiator guard (no anti squeak).
So something, as opposed to nothing, I would say is better. I had to look up Dynamat. It states its closed-cell and due to those tiny pockets of air, I suspect it's good at muffling sound. I wonder how it would hold up to rubbing (I couldn't find an application for that) and if those cells were broken open through abrasion, could it trap and hold moisture? Suggest a google search for anti squeak and you may find a lot of options cheaper than Dynamat, or go "old school" and get some welting! If you choose, welting, call the vendor and ask if its soaked/impregnated with something like oil or tar to help with not absorbing water.