You can submit all your tests, both SAT and ACT. They'll superscore. Of course yo could have dug this out with a little research here: https://www.usna.edu/Admissions/Apply/index.php#fndtn-panel4-Steps-for
Suggest you read the USNA web site including all admissions pages up to the course catalog.
Non sibi sed patriae
It does not look bad to use only one of the tests. Save your money and only send scores that help you. All ACTs scores are converted to SAT scores for the sake of comparing candidates. They really don't make any distinction based on which test you sent. However since they superscore, if sending both brings up your best score on one of the sections, by all means send it.
Actually USNA does! They convert all tests to an SAT equivalent and then use the top scores regardless of which test it comes from. Your highest Math may be from your SAT and your highest English may be your converted ACT verbal score.I do not think they combine test in the super score. They will super score the separate test and use your best one in the admissions process.