Does concatinating mutliple digests of hashes from CSRN result in a CSRN?
Yes it most certainly is, on the assumption that the hashing algorithm used is cryptographically secure and uniform in its output.

As a thought experiment, consider that after Elliptic Curve Diffie Hellman, the shared secret's (curve point) x co-ordinate is recommended by good practice to be passed through a hashing algorithm to derive a key.

This is because the shared secret, whilst a random element of the curve generators cyclic subgroup, may not be uniform key material.

Thus, we can trust that good hashing algorithm's will not erode the underlying entropy of an input (beyond truncation), and should provide uniform output.

Thus I would deduce that concatenated hashes of cryptographically secure input should result in a cryptographically secure output of equal entropy to the input (assuming the hash output length is approximately equal to the CSRN input length).