If you have your layers hosted in a Tile XYZ tiling scheme, you can display that layer within Fulcrum as long as your device has a network connection.
Select Tile XYZ as the layer source,
Give the layer a name
Enter in the layer’s URL
Then set the member permissions
Once finished click the create layer button
The URL pattern style for an XYZ layer looks something like this:
http://c.tile.openstreetmap.org/{z}/{x}/{y}.png
For more general information on adding layers, please visit our adding layers page.
Notes
For your tile source to be compatible it needs to be a "Single Fused Map Cache", have a Spatial Reference of 102100 (Web Mercator), and the tiles 256x256px.
For additional details on leveraging web mapping services, please check out this article.