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I'm not very familiar with H.G.'s randomization technique, so I really
have no idea how well it works.  It sounds like he adds small random
values to leaf node evaluations, which is of course different than
selecting a random 'good' move from the root of the search.

Note that it is definitely true that randomness can be helpful for a chess
engine, even though it might seem counter-intuitive.

For example, basically all strong chess engines (as far as I know) use
random (pseudo-random) Zobrist keys for hashing.  The random keys may be
generated at run-time, or pre-generated, but they are random either way. 
Using different random keys will cause the engine to give slightly
different results without necessarily changing the engine's overall
strength.

Obviously, if used incorrectly, randomness could severely hurt an
engine's strength as well.  For example, if an engine just plays random
moves.  :)