Ableton's Sound Similarity Search works with any sample under 60 seconds in the browser, instrument presets from the built-in library, official Live Packs, and your own samples added to the Places section. User samples are analyzed in the background by a neural network, which is what makes them available for similarity matching.
If you'd rather not have Live running that analysis automatically, you can turn it off under Enable Similarity Search Analysis in the Files and Folders section of Live Settings.