Not really. The iMac is a consumer machine. The MP is a pro machine. A customer considering the top end iMac vs the low end MP understands the tradeoffs. The avg iMac buyer is not going to be enticed by the MP because of the form factor, and vice versa. It's not like a going into a BMW dealer to buy a 328 and getting upsold to the 335. It would be more like going to a dealership to buy a sports car and driving out in a pickup truck.
This is where Apple marketing has utterly succeeded. The Mac Pro is not a "pro machine". It is a standard desktop, that happens to use "workstation" cpu's that are no better than the "consumer" cpu's they mirror. In some cases they are the
same thing. The Mac Pro is just Apple's only real desktop form factor, that happens to have "pro" branding on it.
It's really sad what Apple has done to their own machines. Again, still a "fan" and a user, but when the day comes that PCI slots, and USB3 is considered high tech "pro gear" (do people know how common PCI slots are??)...well that's the day that Apple is either actively killing their own rep, or the apologists are being dumbed down beyond belief.