It depends, I do think they could simply relax the aggregating of “capital” involved and include some Hayekian insights by simply adding some arbitrarily defined stages or production into their macroeconomic analysis whilst leaving their theoretical framework relatively untouched. On the other hand, I don’t think they can correctly reconcile the microeconomic foundations of Austrian capital theory with their analysis, since that would involve (as you pointed out) correctly applying subjectivism.
But I think Caplan’s point was the first of the two.
I need to read Hayek’s work on capital to assess where he falls, but he is often lauded by other Austrians on the topic so I am going to hazard a guess and assume he does maintain a consistently subjectivist stance. Laminustacitus has been reading Prices and Production so maybe he can comment.
I’ve been wanting to read Prices and Production for some time, perhaps Salerno mentions something in the introduction too, since he is originally responsible for the dehomogenization.
If I am of the correct understanding, Prices, and Production is the work that for the first time elucidates a couple of sentances from Mises’ Theory of Money, and Credit, along with the tradition of capital theory from Jevons, Bohm-Bawerk, and Wicksell, into the framework we now know as the Austrian Theory of the Business Cycle; if there was an earlier pubished work, I do not know of it. To reject Hayek from the line of Austrian economists would be utterly moronic in light of works like Prices, and Production, which is a important work in the tradition of Austrian economics, not Hayekian neoclassical economics.