And to my dismay on my itenery next to my partners and my velocity numbers is the tag (MH).
Anyhow, being the first time I'll be attempting a partner airline claim, is this going to blow up in my face? Or is it normal for the FF number to be displayed as such?
Depends on how they've generated the itinerary. If it is a direct printout from the reservation system, then I would expect to see the MH tag on it.
Frequent flyer numbers are entered into the reservation system using an entry such as (not proper syntax)
FQTV<flight-airline-code><optional-sectors-dates-flightnumber> /<ffprogramcode<ffprogramnumber>/<passengernumber>.<segmentnumber>
which allows the system to handle the entry of different frequent flyer programs for different sectors and for different passengers. So, if you had 2 passengers on one booking, and you had segment one being an MH flight BNE-KUL, and segment two being a TG flight KUL-BKK, and passenger 1 had a DJ and SQ frequent flyer program, and passenger 2 had a MH and NZ frequent flyer program, you could have 4 separate entries listed, e.g.
FQTV MH / DJ12345678 / 1.1
FQTV MH / MH12345679 / 2.1
FQTV TG / SQ12345678 / 1.2
FQTV TG / NZ12345678 / 2.2
(again, syntax mangled just for clarity, and because I can't be bothered pulling out my manual)
So, in your case, the MH tag could be referring to the fact that your DJ FF program is the one that is to be "sent" to MH whenever you fly MH.
Or, it could be that the TA has accidentally put your DJ number down as an MH FF program number.
Impossible to say without a raw data dump of your itinerary - not the reformatted pretty version the TAs print off.
As was suggested, best to check with your TA. On the other hand, if your TA is sufficiently incompetent or there's a communication breakdown, you may not get the right answer anyhow. Only way to be certain, ask the TA for a dump from the GDS and either study it closely for one of those formats above, or post (remembering to xx_ out your numbers) here and someone will interpret it for you.