The Kardris tank would have Iron Prison on him the entire time, if it blows up as the boss attacks it could cause issues. If you have enough CDs to ensure he's up shouldn't be a massive problem. It does mean that the Haromm group will get a crap load of Iron Tombs each time, so you'd run out of space a lot quicker. The number of slimes would get pretty high pretty fast if they weren't being killed but with a good kiter would be manageable.
All in all, viable but the issue you may run into is space - the Haromm group will find it pretty busy with all the tombs filling up the area up top and the Kardris tank will have a large and large add group to kite whilst also being targeted by the Toxic Storms and other things he'd usually avoid. If you swapped them round position wise, the Haromm group could faceroll it down south but the tank kiting up north would run out of space even faster.
Personally, I wouldn't use the strat if I had the option to do a more standard split (4/6 or 5/5), but I can't think of a reason that would stop you killing the boss using the strat you've suggested Good luck, let me know how it goes.
(PS: the slimes die in a couple of seconds and the DPS requirement for the boss is super low anyway, the final burn will wipe you if you aren't careful but the enrage itself is a non-event).
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Sorry, I figured that the implication of "Melee can be targeted by tombs" would have been enough! Melee CAN and WILL be targeted by tombs, not necessarily every time, but it's a fully intended mechanic as far as I can tell.