As a general rule, ACS does not provide recommendations of this type, or any endorsement confirming support of an individual's research work. However, you can provide a statement indicating that the individual is a member of the Society and your local section.
"To Whom It May Concern:
This letter is to confirm that [NAME] is a member, in good standing, of the American Chemical Society. Our records indicate that [NAME]’s application was accepted and he has been a member of the Society for X years.
The American Chemical Society was founded in 1876 and has more than 154,000 members. The Society is recognized as a world leader in fostering scientific education and research, and promoting public understanding in science."
Additionally, If the individual is known personally by the officer, and the officer is so inclined, he or she may provide statements, endorsements, and recommendations on personal letterhead, with no indication of office in the Society.