Pretty clear to me that they are not redeemable except physically at a store. I have ordered a lot more from Menards, both train and non-train, were it otherwise. I quote from the Menards acknowledgement email:
"Please note: Rebates are provided in the form of a Menards® Merchandise Credit Check valid towards purchases at any Menards® retail store. Not valid for purchases on MENARDS.COM®. By submitting this rebate form, you agree to resolve any disputes related to rebate redemption by binding arbitration and you waive any right to file or participate in a class action. Terms and conditions available at www.rebateinternational.com®"