stating that the message is electronic
Electronic isn't really a word that gets used in
40k. In this case, it would be put as "a vox transmission".
The mordians report that they have extremely crucial cargo at their outpost and will give it over in return for assistance from the Deathwatch.
Sounds a bit odd put like that. While your players might be "kick in the door and find the loot", Space Marines aren't.
I'd suggest it's more "we have valuable cargo, but we can't defend it much longer. We need someone to take it from us before it's lost." Put like that, it doesn't sound like the Mordians are bribing the Space Marines for help.
Obviously, of course, it's not going to be possible to extract the cargo until the location has been secured, so the players can't just turn up and go "Hi, we're here to take your cargo. Nah, you can deal with that Hive Tyrant yourself.".
Inquisitor Drogan
Is this meant to be the same one from the Space Marine game, because - and trying to put this in a way without spoilers - I would suggest you actually complete the story before deciding whether or not you want to include him.