The API doesn't currently support checking for is_active at this time. I have already previously submitted a request to development for them to add that functionality but it hasn't been implemented yet.
get_xml_host_objects will not list those either as the query that it uses requires an entry in nagios_hosts for it to work and that doesn't exist, development would need to implement the functionality for this to work. I can submit a request to development to see if they will add that to that function if you'd like? Please keep in mind that the decision to implement the enhancement is at the discretion of our development team.