No.
The Dock reflects the running instances of UI applications, as you're a literally running multiple copies of Preview you will see multiple icons in the dock.
Using the open
terminal command with -n
option forces a new instance to be opened. From the the man page:
The open command opens a file (or a directory or URL), just as if you had double-clicked the file's icon. If no application name is specified, the default application as determined via LaunchServices is used to open the specified files. The options are as follows: <snip…> -n Open a new instance of the application(s) even if one is already running.