Don't think it does. Aximand is the one who bears the most resemblance to Horus after all, even being nicknamed Little Horus, but even then i don't think its ever implied any of them are cloned.
It is even mentioned in the current C:CSM that Abaddon may be a clone of Horus.It could be Little Horus actually now that you mention it, but like pb100 I thought it was hinted that Abaddon was a clone in one of the three first hh novels or some vague reference to it. But yeah I have no intention of re reading them either.
The codices are just as 'canon' as the heresy series, and in fact just as much as anything else with a GW or BL logo printed on it. Just because it hasn't thus far been mentioned in the heresy series (if memory serves) doesn't mean the rumour (which has been around for many years now, passing through several chaos codicies) doesn't mean it should be discredited.may be a clone? sorry... no. none of the Luna Wolves were 'clones' of Horus. There is nothing in Horus Heresy series so far to say that any of them are. A rumor in a CSM codex does not eclipse the HH series, which is to be considered cannon.