I think having a drag/drop DMG is probably slightly better etiquite... often what'll happen is the software manufacturer will put an alias (symlink) into the DMG with their logo in the background, and you can just drag whatever directly into the resources folder, unless you're actually sprinkling stuff into other folders on the system.
It's just a little easier to drag-and-drop than running an installer. It's kind of considered a "Don't do it unless you have to.". I know, we're picky. ๐
Here's an example of what it could look like:
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You could also put the orange spine on the Disk Image icon if you wanted to get really fancy.
Here are some links to explain how it's done:
For setting up the folder view settings and disk image icon:
http://el-tramo.be/guides/fancy-dmg/
For setting your background image:
http://iconfactory.com/home/show/1152