Huffman encoding of hashes
A cryptographic hash function will produce an output with pseudorandom properties, therefore when expressed in hexadecimal, a list of hash values will have an almost equal number of each character. Pseudorandom data will not compress, as compression looks for patterns. If you had duplicates, compression could reduce the data size.

If you want to compress the list, take your hexadecimal string of 32 characters, and convert it back to ASCII character values, taking up 16 characters. If you need it to be text readable, that can be encoded using Base64 or a variant, which will take 22 to 24 characters.