If this story is true, it would represent a transformation as to how we’ve understood the role of the civil service and its head, not least that we’re not supposed to know how they’ve voted about anything. 
If, as the article says, No10 wants to recruit civil servants on the basis of their political views (ie being Brexiteers) then they’ll have to change the civil service code, which in various places, is very clear that that isn’t really permissible.
Tbh for a whole bunch of reasons, I doubt they’re serious about this/is possible and this is more likely just a bit of signalling to the Leave base.
