Let's get straight to the point. Does Ubuntu's Unity desktop use its own panel? I mean the sidebar that has the icons and the dash. It would have to be, somehow, a panel. And if it is, is it possible to implement it in a different desktop environment, like, say, a custom Openbox session? Also, could we use another panel, say, tint2 or pypanel or even lxpanel, with Unity? Considering Unity is a GNOME fork, and GNOME uses its own panels, this would make sense. Even if it would be impossible to actually utilize the Unity panel in Openbox, couldn't we at least add the program name (something like "unity-panel") to a desktop configuration file in /usr/share/xsessions?
The main issue is with the workspaces (multiple desktops), which in Unity are implemented quite differently from those in Openbox/GNOME: Unity uses a huge desktop divided into multiple smaller ones, and whether a window belongs to a desktop depends on its coordinates. Openbox and GNOME show the desktops as if they are stacked on top of each other, with only one visible; whether a window belongs to a desktop depends on a tag.
Also keep in mind that behind the scenes, Unity uses Compiz as window manager, not the window manager from GNOME.
Thus you can use in Unity any panel that is able to interact properly with Compiz. Tint2 can do that. I don't know about the others.
If you don't use multiple desktops, most panels might work well for you.
About using the Unity panel in Openbox, I do not know.