Yes, you can! Public, non-secured SLIP web services can be added to ArcGIS Online. ArcGIS Online supports a number of data formats including web services, OGC, and data uploads.
By design, ArcGIS Online supports ArcGIS token-based authentication. Unlike some desktop applications, credentials are not stored in ArcGIS Online for secure services that utilise token-based authentication. At this stage SLIP only supports HTTP Basic Authentication, but we are aware of the desire to support ArcGIS token-based security and are actively investigating the technical changes required in 2017.
In the meantime, there are a few workarounds available for using secured SLIP web services in ArcGIS Online.
Run a Resource Proxy
Running a resource proxy involves configuring and setting up a small web service that will proxy or pass through requests made to it to SLIP. This allows you to securely store your SLIP credentials in the proxy service, which then attaches your credentials to all requests it sends to SLIP.
For example, if you setup your proxy at https://mydomain.com/slip-proxy-imagery/ and configure it to point to http://services.slip.wa.gov.au/arcgis/rest/services/DOP_Restricted_Services/DOP_Restricted_Services/MapServer, you would then be able to add add https://agency.wa.gov.au/slip-proxy-imagery/ as a web service directly to ArcGIS Online in order to load the Landgate Subscription Imagery service without being prompted for authentication.
There are a range of proxy options available (.NET, Java, PHP, Python, et cetera). Note that ESRI's own Resource Proxy at this stage does not support the authentication system used by SLIP (HTTP Basic Auth).
In implementing a proxy you should carefully consider the environment in which you're using it, and the implications of making an unsecured proxy available - particularly if your ArcGIS Online map is public. Please contact the SLIP team for advice if you are planning to setup a resource proxy.
Save credentials in your web browser
When adding or using secure SLIP web services in ArcGIS Online, users must first authenticate against the service in their web browser. ArcGIS Online does not always prompt users for a username and password.
This workaround is generally only suitable where there are small numbers of internal users accessing the service, and where they all have separate SLIP accounts, or where they share the credentials of a single SLIP account.
Upload a data snapshot to ArcGIS Online
SLIP also provides a number of options for downloading available data, including shapefiles. Users can download data to their desktop and then add data files to ArcGIS Online to create content, taking note of any applicable data licenses that may restrict use and distribution.