Neither Nvidia nor AMD list professional graphics shipments separately these days. Professional, discrete, discrete custom ( FirePro D series), and discrete mobile (MXM) shipments are used in both Mercury and JPR's figures.
AMD's professional board figures aren't a straightforward extrapolation of market share as the consumer market largely is. Nvidia boards sell at vastly greater ASPs. To use the "MAC" (Mac Pro) example you cited:
The top Mac Pro comes standard with Dual FirePro D500's and can be upgraded to Dual FirePro D700's for $600.
The FirePro D500 is a custom part analogous to the HD 7870XT ( so sits between the Pitcairn-based FirePro W7000 and Tahiti PRO- based W8000) The W7000 is priced at around $600 each, the W8000 at ~ $1000 each
The FirePro D700 is a FirePro W9000 (also in a custom form factor as per the other FirePro D boards). The W9000 retails for around $3000 each......and Apple offers an upgrade to two of them - from boards priced at less than $1K,
for $600
Given that Apple has to factor in their own profit and amortization from warranty replacements, how much do you think AMD's unit price contract is for these custom SKUs?
AMD basically purchased market share (and the cachet of marketing by being allied to the Apple Mac Pro). If AMD rely upon this business model, they build market share all the way to the poor house.