The answer from support is, "No, they will not provide a letter of exclusive use for an IP because if I destroy the droplet the IP is no longer exclusive use.". I understand this and explained how it is in my best interests to remove those IP's from my account with Microsoft's Junk Email Program if a were to the destroy the droplet in order to keep my own reputation from suffering due to the next owner of that IP. I fail to comprehend Digital Ocean's stance - if they say, "As of x/x/xx our customer so and so has exclusive use of this IP." - This is good enough for MS. How is this a problem? When they write the letter it is a true statement. If I destroy the droplet tomorrow it doesn't make it any less true than the day they provided the letter.
Oh well....I tried.