Sorry if this seems an silly question but I'm new to target. I was wondering if we can create custom segment / audience in Target by importing some user account numbers, which aren't tracked in Adobe Analytics. The account numbers are passed to the datalayer once the user is authenticated. So, is it possible to use some account numbers that are only available in the datalayer and trigger a campaign if the condition are met?
You can set it up in the DTM interface so that it passes parameters from the datalayer through DTM to the mbox. However, there can be a problem that causes the mbox parameter to be empty. The problem with most implementations, is that Target loads at the top of the page before the datalayer loads. Which means that when Target loads, the datalayer isn't yet available. So even though you did it correctly in DTM, you will get an empty value. I have written more on that here. http://www.modus73.com/method/problem-mboxes-datalayers.
So it can be done through DTM and a datalayer, but you must make sure that your datalayer loads before Target.
The best way to do it is as Jason mentioned and linked to above. You can pass parameters to Target through a function called targetPageParams. This is setup as part of your implementation and is done server side, so its not actually done through a datalayer.