Dear JR,
Shankara Digvijaya does mention about Skanda taking birth as Kumarila Bhatta.
In fact it states that his birth as Kumarila Bhatta is for the revival of the ritualistic section of Brahma(the Veda) and hence by known as Subrahmanya(promoter of Brahmanya).
I have not read Sankara Digvijaya.
In taittiriya Aranyakam, Indra is addressed as subrahmanya.. The verse is:
subrahmanNyom, subrahmaNyom, subrahmaNyom
Indra AgacCha, hariva agacCha mEDhathiThe (T.A. 1.58.9)
Bhatta Bhaskara in his commentary has given the meaning as : SoBhanam brahma, subrahma vedaH
In Aiteraya brAhmaNam, the assistants to Hotrs were called/addressed as subrahmaNya.