I would assume that it is possible to transport a wormhole end via a wormhole, if the wormhole end has a "deactivated" state, in which there is no hyperspace connection present.
One would have to assume that the wormhole end is transported in that deactivated state, moved to an appropriate location (eg no gravity gradient), and then "switched on". While it's in its deactivated state it may be just another chunk of machinery with no special requirements, and thus can be carried through a wormhole.
However, there may be some kind of pre-connection (enough to maintain the connection between point A and B, but not big enough for something to travel through) through hyperspace which is maintained during the voyage. If this is the case, then it probably wouldn't be possible to send the portal through a wormhole.
The point @Richard makes about multiple wormholes between systems, to more easily recover from portal destruction, would make a lot of sense either way, as would a large degree of redundancy, eg five wormholes per system. The only possible reason i can think of why this wouldn't be the case (whether "portals-through-the-wormhole" is possible or not) would be that the wormhole creation and transport is so fabulously expensive that the Mercatoria can't afford to do it.