I'm fully aware, I did that on Xubuntu before Thunar got tabs (I just waited to switch because there were some things I didn't like on PCManFM. Specifically, the way it handled file moving, I don't know if it got changed). But that wouldn't be "running LXDE" at all, it would just be changing your file manager.
And yes I guess you'll be able to run pcmanfm-Qt on Unity Qt, if only you find yourself on that machine and want to quickly install that file manager without messing anything up. Some people run pcmanfm GTK2 on heavy desktops.