The amateur rule is for those showing USEF. Any and all USEF shows follow the amateur rule. If you are getting paid to ride but not horses… what are you riding?! If you mean can you ride your own horse (absolutely) and get paid to groom then yes, you can (GR1306i). However, see rule GR1306-4c and you can see that if you accept remuneration AND groom AND ride/train/school horses for an employer (your trainer that you groom for and accept remuneration from)/employers family/business where employer has ownership interest [narrowed down from a long description to fit the situation you described] you are considered a pro.
For further explanation of the USEF Amateur rules please see https://www.usef.org/forms-pubs/nT3T…rticipants-and - rule GR1306.