I reject the question of "is that okay?" I only submit whether the definition of spam is accurate.

Your characterization of a transaction that is Open time stamped is not accurate. It is a financial transaction that is used as a timestamp proof. Like using a decentralized checkbook to prove you were in the store writing the check at a given time. The transaction is a transaction, the OTS correlated is coincidental.

Again spam is when a field is exploited beyond the necessary data to make the transaction. OTS embedding doesn't add extra data and therefore burden on others.