Hi John ,
From your description, it appears that you have shared the audience from Marketo to experience cloud (which is related to AAM in backend, you dont necessarily need to have AAM license to be able to share the audinces).
So if the audience has been shared to experience cloud successfully, you should be able to find this audience in People > Audience Library.
Once the audience is available in Audience library as mentioned above, it should be visible in Target UI > Audiences , with the source as experience cloud.
Let me know if that helps.