I'm a new customer and have installed 5.0 "over" 4.2 per the documentation, but now the recorder just hangs. Someone on my team installed 5.0, having no previous version installed, and is able to record with no problems.
What do you mean by "over"? Did you overwrite the 4.2 installation folder by 5.0?
If yes then i would recommend you to install again NeoLoad 5.0 on a separate folder and try again your recording with that version.
To answer your question, having multiple NeoLoad versions installed on the same machine is not an issue as soon as they are installed on separate folders.