No, cerveranums are quite variable, but nonetheless distinct.
The staminode and pouch are different. In cerveranum the staminode is finely pubescent (in appletonianum it is glabrous or waxy smooth) and it has a central apical tooth (apical in this case means pointing downwards) and tucked in, backward pointing, between the labellae at the back of the pouch. The pouch is very different; in cerveranum the pouch has a ciliated rim and is of thinner substance, usually with more prominant veining, and is typically more "inverted" helmet shaped. In appletonianum the pouch is of heavier substance, especially noticeable at the rim which is thicker and lacks cilia, and it's usually more vase shaped. For example the album appletonianum that cxcanh posted here http://www.slippertalk.com/forum/showthread.php?t=45786 is typically cerveranum like, but I cannot see the staminode clearly enough to confirm. I think cerveranum ought to be more widely recognised as a separate species, when you've grown both the difference is clear and simple. It is possible that these two have already been crossed and so intermediate forms are possible. cerveranum is synonymous with robinsonii, which Cribb thought to be a hybrid with hookerae. The ciliated pouch rim and pubescent staminode are indeed features which cerveranum shares with hookerae and some other barbata species, but neither appletonianum nor bullenianum have these features.