BLAS1-type operations on vectors

Does anybody know what is MATLAB using for performing BLAS1-type operations, e.g., dscal or daxpy?

>> a=ones(1,1e6,'double');
>> b=ones(1,1e6,'double');
>> a=2*a;  % dscal
>> a=2*a+1;
>> b=2*b+a; % daxpy

I have substituted MATLABs BLAS library using the BLAS_VERSION environment variable. I used a custom compiled (and modified) OpenBLAS, and inserted some printf here and there to see if MATLAB is calling the library. I do get a printf for matrix-matrix multiplication, but I do not get anything for the simple BLAS1 operations. Which is a shame, because I really need this for performance reasons.

Which makes me wonder - does MATLAB re-implement this basic functionality? What would be a reason for doing so? And finally - where is it implemented and can I pre-load/substitute it?