I'm sure if you asked the guy he'll give you the code, but keeping the code concealed may be a good thing because it'll stave off the bot being compromised for some time.
Yup. You really think that Wiki folks would keep it quiet if there wasn't a plausible reason? Come on!
We already have several open bot frameworks, it's purportedly an easy task to whip up a vandalbot. There's even a similar transclusion-checking bot that was made open source. And surely making MediaWiki itself open source was even more dangerous, and yet, there you go.
And finally of course there's argumentum ad Jimbo.
Dan