Hello maresca and welcome to the forum.
It is true that debts run up due to gambling are frowned upon, but that in itself is no automatic bar to looking at an IVA. My personal view is that if you can prove that you have sought and are taking profesional help for it then I would be happy to have a stab at it under those circumstances. You could always have a DMP as a back up, if you wished, if the proposal was rejected.
That said,I can also see the sense in proving yourself, so to speak, for a few months to prove that the habit has been well and truly kicked so a DMP is not a bad option.
It IS true that generally professional DMP firms will take the first payment as a set up fee, but there are firms out there who, if an IVA was sucessfully proposed a little later on, would then release the first payment on the DMP to kick start the IVA, in effect your IVA would then be 59 months instead of 60. You may wish to look down that route so no harm in speaking to a few people.
Ultimately though, the contribution to either DMP or Iva is determined by affordability, so if you have a healthy disposable income which will clear your debts in a reasonable time, then creditors may prefer a DMP over an IVA. Again, no harm in taking 2 or 3 opinions on this.
Hope this helps.
Regards.