I am trying to open a file in a new tab in an already running console Vim session. This functionality is available in gVim via the --remote-tab-silent option. If this is not possible, I was wondering if there is a work around.
If you have Vim compiled with +clientserver, and you run Cygwin's X server, and you invoke console Vim with a --servername argument, then yes. See:
When you install Cygwin's version of gVim, it should create a symbolic link from /bin/vim to /usr/bin/gvim, which means you will have +clientserver and you can use this functionality in console vim.
The reason the X server is required is that "Unix" variants of Vim use X's security protocols and interprocess communication to implement the +clientserver features. The question is whether you want to have to run Cygwin's X server just to get this functionality.