Interesting question. Are you asking if there s a legal difference between using a recording of a person singing vs speaking? There isn t, but a lot depends on the source and the content of what they re saying.
In copyright law, a recording or arrangement is treated separately from the actual song or content. Even if you use random words to avoid copyright infringement of the content or song (or spoken words), the recording itself is covered by copyright. For instance, if you used a recording of an actor reciting a poem, both the poem and the recording hold two separate copyrights. By choosing random words, you may avoid copyright infringement on the poem, but the recording itself would still be covered.
I *think* an exception would be public figures like politicians. Their public speeches assume consent to be recorded and reproduced. If you made your own recording of (for instance) the President and sampled his words to create a song, that would be legal.