While you could do this, the warning is that if the photos are not the proper format (size and filename), the camera can corrupt the memory card.
Normally, when a camera uses a memory card, it will create it's own folder (under the DCIM folder), This allows you to use the same card with more than one camera as each camera creates it's own folder. This practice was intended to be done when the standards for camera cards were developed.
I have 6 different digital cameras, and contrary to the advice above, I use them on all of the cameras without any regard as to which one goes where - and I have yet to have any problem with any memory card issues.
The reason this works is that each camera uses it's own folder, and no camera knows about the other camera as it doesn't care what is on the card outside of it's own folder.
However, I do NOT use one camera to view the files created from another camera on the same card, as that IS asking for trouble (corrupt card, lost files, etc). To do that, you would have to copy the photos from one camera's folder to the other, but I am not recommending you do that, as again, if the camera cannot properly recognize the files or the format, it can corrupt them.
However, the advice above about not using the SD card as permanent photo storage for a camera I agree with as best practice. Use the SD card chiefly for taking photos and transferring them to your computer, where you can maintain multiple backups of them.