I do not consider that the feature working however.
You are basically saying that the Dark Powers know of the contact (the feature says exists), lure the character into thinking they can get a message to that contact (even though that is a ruse) and then use that to trick the character into something.
How is that at all what the feature says the character can do because of it?
OK, the feature says that your contact who acts as a liaison to a network of other criminals.
The Dark Power provides the contact--or a facsimile of your contact. Or even a brand new contact who has something that identifies them as a friendly--for example, in the contact's guild, everyone has a certain tattoo or uses a certain password.
Obviously you can have a new contact with this feature, because otherwise it would be suggesting that your contact is unkillable and always available, or that if your contact is killed or jailed your background feature becomes useless forever. I'm pretty sure that either of those two options wouldn't make much sense as a rule, yes?
Next, the feature says that you know how to get messages to and from your contact. I mentioned a dead drop. There are certainly other options, however, especially if you get magic involved. ("See this wanted poster? Burn it. That means you want to talk to me. I'll know.")
The feature says you know the local messengers and others who can deliver messages. Still possible. Your contact says "I see you're heading to Vallaki; if you want to get in touch with me, give a note to the Milos who hangs around outside the Blue Water Inn. You'll recognize him by the three scars on his right cheek and his big yellow hat. Tell him 'swordfish'. That'll let him know to give the note to me. Be sure to give him a big tip."
Then, should the PCs go to Milos, he might mention someone else who could potentially be another contact or messenger--to pull from earlier editions, the Red Vardo Trading Company. Or if the DM doesn't feel like reading up on Ravenloft history, they could make something else up. Or maybe Milos doesn't say anything, and you have to wait for the contact to point them at more "local messengers, corrupt caravan masters, and seedy sailors." Or you start asking likely people if they know your contact and start establishing connections.
See, the background assumes you learned about the innkeeper and password at some point in your past. Instead, since you're mysteriously in a new land, you're learning about them
now.
And no, not just
anyone can do this--a criminal contact wouldn't give just
anyone this information. Because you're a criminal, the contact knows that you're One Of Them. Additionally, the Dark Powers, always looking for a hook, would make a contact for you.
Now, if instead of going to Ravenloft, you wound up in Greyhawk or Eberron instead, there won't be any mysterious beings who rewrite reality in order to spread horror. Instead, there's one of two possibilities. (1) The criminal PC has to work to establish contacts. (2) The criminal PC commits some crimes and gets noticed by one of the thieves' guilds or the Boromir clan or whatever; I don't know that much about either setting.
And again, not just
anyone can do this. The criminal is going to be establishing contacts or committing crimes (not just standard PC unruly unlawfulness, but actual, literal
crimes) in a way that will alert other criminals that you are, again, legitimately One Of Them. A fighter with a criminal background is going to have a certain something about them that a rogue with a sage background won't.