I think your letter is fine! Like @ABC mentioned, include letterhead or logo, manager signature and contact info.
I personally don't think you need this:
“JH has demonstrated good behavior and professionalism in the short amount of time that he has been with the company.
We request that JH be permitted to enter United States of America by granting him a US Waiver.”
My letter from my employer was simply 3 lines giving ARO what they asked for.
There are opportunities to explain your situation in the other letter you need to write that explains why you did, what you did and how remorseful your are. Plus opportunities for your references to back up your character.
In the end, up to you on how much detail you need your employer to add to the letter.