I dug deeper into the issue thanks to the information given by Chealion. While it is true that the manual do imply that the checkbox to Enable Server Group Mailing Lists should work to solve this issue, it became quite apparent after a while that Apple decided to not have mailing list administration as part of the open directory.
As far as I can tell, the reason is to avoid having to need administrator access to the server to set up such a thing as a distribution group. Also, if I understand correctly, the connection with the Wiki is in order to provide further collaboration tools. In fact, the collaboration framework is actually quite nice. The wiki provides a one stop shop for gathering semi-permanent information, while also enabling the addition of a blog service, calendaring as well as the infamous mailing list. This quite neatly gathers many of the aspects of digital information flow required in a modern project environment. The interface is easy to use even for non-technical people and while there aren't a ton of features, most of the fundamental features are readily available.
However, while the system is quite nice, there's still the matter of the weird e-mail suffix: -wiki. For some reason, Apple chose to append said suffix to the shortname of the group (wiki, som discrepency in their naming scheme there). However, upon investigation, I noticed that the suffix is little more than an arbitrary naming scheme with very little impact on the actual functionality of the system. I assume this was done for some odd reason such as not confusing the name of the wiki mailing list with a proper user or mailman mailing list, but that kind of reasoning is so far fetched that I must say that I honestly just don't know.
In any case, it's quite easy to patch the wiki to get rid of the suffix. There are two files that need to be edited in order to make this work.
/usr/share/wikid/lib/python/apple_utilities/MailUtilities.py
Change line 263 to look like the following code:
mailAddress = entity.shortName
Change line 465 to look like the following code
groupMailingAddress = u"%(groupName)s@%(hostname)s" % {'groupName': groupName, 'hostname': hostname}
/usr/share/wikid/lib/python/apple_utilities/MailBundler.py (possibly optional)
Change line 55 to look like the following code:
group = group.replace('-wiki', '')
You then need to remove MailUtilities.pyc and MailBundler.pyc (found in the same directory) and compile new ones using the following command (don't forget the dot at the end):
python -mcompileall .
After doing these edits, restart the wiki and the -wiki suffix should be gone. I had to go into each wiki and make some a change to the permissions (any change will do, remove and re-add a user for instance, it's just to enable the save button), then save the changes to force a regeneration of the postfix aliases file. Any subsequent changes however, addition of wikis, removal, permission changes etc works just fine. The great part about this hack is that it actually both give you friendly e-mail addresses for your mailing list, and it also works with the online mailing list feature in the wiki web interface.
Hope this helps anyone!