In Dolphin (and Kate), I can see my GDrive under Places. However other apps that use the file dialog (kdialog?) do not seem to show the Remote Places. So I was hoping to navigate from root, but I cannot find my GDrive.
Entering gdrive://maparillo@gmail.com/ into the file dlalog as the starting point as the gdrive Help Center article seems to suggest does not seem to do anything either.

Kio doesn't mount remote drives, but instead provides network transparency to Kio-enabled applications.
There's been some recent discussion about having Kio provide mount points for remote drives: viewtopic.php?f=83&t=141917&p=408246

You should be able to browse the GDrive by entering the full URL into KDialog: In both KDialog and Dolphin you can click on the empty space in the path bar to switch to Edit mode. This will allow you to see and enter the full URL to browse, even if the location hasn't been added to your Places. You might double-check which url to use by opening Dolphin, opening the GDrive, switching the path bar to editable mode and then copy the URL that shows up into KDialog (KIO may use slightly different urls for certain services).
If copying the url from Dolphin into KDialog doesn't work to open the files in KIO-enabled applications, that would be a bug and should be reported on bugs.kde.org.