Using the raspberry pi camera is there a url that can be used to grab a still shot? Similar to https://www.raspberrypi.org/documentation/usage/camera/raspicam/raspistill.md but it would need to be done on a remote host
This can be done, but it isn't as simple as if you were interfacing with the RPi itself. You will somehow need to signal the host RPi to take the picture, and then return it to the client.
The simplest way would probably be to use a website you host on the RPi, but a tutorial on how to do such a thing is well outside the scope of this site. I would suggest googling the problem and looking at similar projects.
If you want do be able to do this using an URL, you will have to build some sort of (REST) API.
Chances are that sombody has already done this in the past.
A quick google search showed me this one.