From what I can see in the most that you can get is something like $0.015 cents per point if you use it for travel, but you only get one point for every $2 of debit purchases.

https://www.rewardsnow.com/texans/tr...?categoryid=11

We are talking about $80,000 worth of purchases for a domestic ticket not costing more than $400.00 {Your financial institution might have different redemption tiers as the program is independently run and marketed to small financial providers where managing their own program would be financially unfeasible}

Not a lot of value for a lot of work, but now to your questions.

Is it ethical? There might be a few who disagree, but I think is ethical as you are not doing anything outside of their rules.

Will the credit union lose money? Probably not even if they only charge 1% to the merchant for a debit transaction, that is probably how much they are paying the rewardnow people. Remember it takes $2 to get a point.

Can this be considered abuse? Yes it can specially if you are moving large amounts a month. It will be completely up to whomever is running the program in your credit union. Once they have to start paying rewardnow thousands of dollars a month, they will take notice specially if they are small.