I just tried it but doesn't work as I originally expected.
When I enter "vs" in the terminal, it starts SlickEdit but the terminal isn't available until I quit SlickEdit. This doesn't happen when I enter "&" at the end, however I keep forgetting to add it. Also if I press "CTRL+C" while SlickEdit is running, it is terminated without a prompt to save any changes, thus there is a chance of loosing my work. When the screen was in full screen originally, starting it from terminal restores it to a normal window. And lastly, executing the command when SlickEdit is already running, displays "Identified already-running instance of SlickEdit" and in some cases that never returns, even if I quit SlickEdit. If I start SlickEdit as sudo it is like running SlickEdit for the first time and all settings isn't available. That doesn't happen when I use TextMate.
What I was expecting was that when I enter "vs abc.txt", that "abc.txt" is opened and I have further access to the terminal for more commands. When I enter "vs def.txt" then def.txt will be opened in SlickEdit, and I have further access to the terminal. It would be great if I can have multiple instances of SlickEdit open similar to TextMate and Visual Studio. I often open several solutions/workspaces/projects at the same time as my codebase consists of several solutions/workspaces/projects.