This looks like a good addition! There's some style things to fix up, and there's a nice trick you can use, but the logic looks generally fine.

Imports must be alphabetized.

Two blank lines between classes.

I know some older classes don't do this right, but this should be:

super(Column, self).__init__(_('Bugs'), ...)

No space before ':'

You can actually simplify this with the very neat Python generators:

return ','.join([
    '<a href="%s">%s</a>' % (bug_url % bug, url)
    for bug in bugs
])

This should include the format, and ideally say "... when rendering bugs column". So:

logging.warning('Invalid bug tracker format when rendering bugs column: %s' % bug_url)

Two blank lines.

Alignment issues.

Make sure you're not using tabs in any code. It should always be 4 space indentation.

No need for the \, since it's in parens.

We can just unconditionally return this at the end. No need to do it once in the exception handler and once in the else statement.

Can you make the = align with the other columns?

This looks good in general, but one thing I'd like to see is the links become blue and underlined in the dashboard, so it's clear they're clickable.

You can have a class for the column and use that to key off the CSS.

Alignment issue.

Probably should be ", ", actually. A space will make it look nicer, and will allow it to wrap if there's a large number of bugs.

Blank line between these.