Unfortunately, I don't know if you're doing the right thing or not.
For more or less simple cases, I can give advice on a short description of the problem.
But this is not your case.

1.  Have an AR Camera where all the user sees is the 3D markers (via map) within AR scene. I have this working using Tileset.

2.  Have a slide-in map where the user can zoom, pan and rotate the Map.  I have the slide-in map working using ortho camera (NOT Texture on UI/Canvas). What I am trying to do is add the ability for the user to zoom, pan, and rotate (cameraOrbit) while the Map is in view.

3.  When map slides-back-out-of-view (user is back in AR world) the Tileset map/3D markers from step #1 are exactly as they were  (before any changes were made by user zoom/pan/orbit).

To accomplish step #2 I added the Map Camera to the tileset map and give User Control and Zoom, plus added CameraOrbit component.  By "assigning" the Map Camera to the tileset, I started receiving the frustum errors, which is why I created this post. 

I spent a little time looking at the Tileset with Map Camera UI tutorial.
...and before I make a hot-mess of everything I thought I would check...
...just want to make sure I'm doing things the write way; I tend to make things way too difficult.

Thanks.

Try this (OnlineMapsTileSetControl.HitTest):

protected override bool HitTest(Vector2 position)
{
#if NGUI
    if (UICamera.Raycast(position)) return false;
#endif
    Rect rect = activeCamera.rect;
    if (rect.width == 0 || rect.height == 0) return false;
    return cl.Raycast(activeCamera.ScreenPointToRay(position), out lastRaycastHit, OnlineMapsUtils.maxRaycastDistance);
}

I have a Map Camera which slides in from the side of the device.  I use a Tileset control in my AR App, and map not visible to the AR camera via the culling.  So while the Map Camera is out-of-view, I get the following errors:

Screen position out of view frustum (screen pos 0.000000, 0.000000) (Camera rect 0 0 0 1024)
UnityEngine.Camera:ScreenPointToRay (UnityEngine.Vector3)
OnlineMapsTileSetControl:HitTest

I'm curious what is the best way to tackling having the map slide-in/out without getting the errors?  My thought was to disable the map renderer, till the Display Map Button is clicked.  Then, turn on renderer AND start camera slide into view.  I do think there is a possibility of a few errors each time however, due to the renderer being enabled slightly before camera rect is updated.

What do you think?

EDIT: Maybe it would be better to switch between Main-Camera and Map camera (and back again) based on if the Display Map Button is clicked.

Thanks.