Yes, you can!
If you have multiple WordPress.com sites under one account, they will all show once you log into the app using your WordPress.com credentials (username or email address associated with your account and your password).
To add self-hosted sites, once logged in with one site, select the My Site tab at the bottom right corner of the screen and select the Switch Site option at the top of the screen if you are using iOS or the arrow beside your site address for Android.
From there, select the + icon and you will see the option to Create WordPress.com site or to Add self-hosted site.
The Add self-hosted site option will request your username, password (the ones you use to log into the wp-admin area) and site address (starting with http://).