Is there a 'standard' means to detect Eigen types with SFINAE/enable_if, provided by the Eigen library itself? I could probably check for the existence of things like T::RowsAtCompileTime, as these aren't likely to be present in other types, but I'm curious if there is an officially supported way of doing this? In short, I would like to distinguish types provided by Eigen from all other types.

There is no such Eigen signature, but you can make your function take an EigenBase<> instead of a fully generic template type.