How can I open a file in DVT from the terminal?

You can use the Command Line Interface like this:

dvt_cli.sh -workspace ~/dvt_workspace openFile $(readlink -f my/file.sv)

The command can be shortened by defining this alias in your ~/.cshrc:

alias dvtopen 'dvt_cli.sh -workspace ~/dvt_workspace openFile `readlink -f \!*`'

or by defining this function in your ~/.bashrc:

dvtopen () { dvt_cli.sh -workspace ~/dvt_workspace openFile $(readlink -f $1); }

Then the command gets much shorter:

dvtopen my/file.sv