It is definitely possible to do something like this through the UA API!
The reason why we recommend using no more than 1000 selectors is avoid timeouts. The larger the amount of data you try to send through the internet, the higher the chance of a timeout.
So, you might be thinking "How do I message x amount of users in the API?"
The primary way we recommend to do this is through the use of tags. Coming from Parse, you may have also seen these in the form of Parse "Channels". You can use those same "channels" as tags within Urban Airship to group a list of devices together to send a push to.
Now, you can also send to an array of devices, like you mentioned, but if your audience list is more than 1000, you may end up having to split the array into 1000 device parts. So, if you have 2000 devices to send to, you'll have two separate api requests to send to the first 1000 devices, and the last 1000 devices in the array.
Definitely take a look through some of our Example API requests if you want to check out how some of the requests can be put together.