Not using either, but I can offer some suggestions:
I inspected /usr/share/applications/lxterminal.desktop, and found the icon specified as
Perhaps docky is not looking in the right place for the icon. I honestly don't know where docky expects to find it. Have you tried putting a copy in /usr/share/icons? How about in ~/.icons? Both per the xdg spec, however /usr/share/pixmaps is per the spec as well and should work. To not have copies all over I'd symlink rather than copy, but that's my own personal preference.
Perhaps the theme is messing things up. Try
https://wiki.archlinux.org/index.php...ns_and_emblems, see if that helps.
The last thing I would try would be to edit the .desktop file to specify the icon as an absolute path. Of course this will likely break in the future. As an alternative, copy the .desktop to .local/share/applications and edit it, and replace your current launcher in docky to your local copy. This may be more immune to future breakage.