Humm, there was a thread about DRK/BST on alla not to long ago and that is actually something I have been wanting to try for some time, just need to level BST to an approriate sub level
From the informations I gathered while researching BST, your charm success is determined by your CHR vs the mobs CHR (The higher the mob, the higer the chr), AT THE TIME WHERE YOU USE CHARM!!! This is the key to DRK/BST. Find a DC mob or EP to be sure (at least the first try) and cast Absorb-CHR. It will increases your charisma by 5 and reduces hte mob's by 5 (at my level anyway), creating a 10 points gap. Combine that with proper food and +CHR gear when you charm (gear swapping) and I say you probably have a pretty good chance of charming, even if the first spell generated some hate.
The duration of the charm is determined by the level of the mob compared to you. So if you succesfully charm a pet, you do not have a greater risk of seeing the charm break then a regular BST.
Nice thing with DRK is you have a lot of ways to kill your prey fast. Charm, send your pet, watch the show or heal, cast some spell to help your pet if needed, try to have your pet killed when the mob has just a sliver of heatlh left, Last Resort (and maybe Absorb-STR at the end, should not get hate if the fight has been going on for a while) and slash the mob in half in one quick Scythe strike.
Anyway, this all looks good on paper but I have not tested it yet. I'll let you know if I ever do!