Hm, I guess he'd just place the zoom a bit farther away (even quite far) from the amp so it picks the sound a little later and also some room sound, and then feeds back the Zoom's output to a mixer - so you get a reverberated sound in addition to mix in. Or maybe the zoom has a reverb built in as well, go figure...but sure you can get reverb with any mic placed well off the amp and mixing it with the original.
Only, you'll also get all kinds of bleed from any other instruments plus noise plus phase issues...so it's not the way you'd usually do it live, only in recording.
Dee
"When life's a biatch, be a horny dog"
Amps: Marshall JVM 410H w/ Plexi Cap mod, Choke Mod & Negative Feedback Removal mod, 4x12", Behringer GMX110, Amplitube 3/StealthPedal
Half a dozen custom built/bastardized guitars all with EMG's, mostly 85's, Ibanez Artwood acoustic & Yamaha SGR bass, Epiphone Prophecy SG, Vox Wah, Pitchblack tuner plus assorted pedals, rack gear etc. for home studio use.