Backup of Databases not present in Availability Groups
It really Depends,

Technically, as others have mentioned, you can use one built in maintenance plan to backup all of the databases.  Regardless if they are in an AG or not in an AG.  

But having it all in one plan, and having that plan fail, means you may miss some SLAs.  There is a question I ask myself when setting up backups:  "What is the Restore Strategy and the SLA?" Your backup strategy should account for your restore and recovery requirements in the SLA.  Can you restore exactly the amount of data that business requires, in the time frame required?  Imagine if your one maintenance plan fails, and only backups up half of the databases one night. What happens if a disaster occurs between the failed backups and the next backup cycle?  Can you recover the data and get the business back online?  It depends on your SLA.  That should help you decide if you need one job, two jobs, or a different strategy entirely.

Also Since you mentioned,  "Do i need to use copy_only?", am I right in assuming you have Databases acting as principals/primaries, and other in an AG group acting as secondary replicas?  If so you can still techincally use one job but you need to understand what copy_only does. The article has some good highlights.