I'm not a fan of White Herb, seeing how it can be reduced to being useless by a simple Intimidate. If you want an Arcanine that really leads well in NB, try this.
Arcanine (M) @ Choice Band
EVs: 252 Atk / 60 Spd / 198 SAtk
Lonely Nature (+Atk, -Def)
- Hidden Power [Fighting]
This thing is much sweeter than you think. OHKO's on Tyranitar with HP Fight, Dugtrio, Alakazam and Ninjask with Extremespeed, and 2HKO's on Snorlax and Blissey with HP Fighting. Double Edge > Return if you wish. Overheat / Fire Blast > Flamethrower if you wish. I found Flamethrower to be effective enough. This is also 240 speed, which outspeeds practically all Metagrosses. You can toy with the EV spread if you wish.
Cradily looks fine. I'd prefer that over Umbreon. Lefties > Lum I'm thinking. Also 252 / 252 / 6 spreads tend not to be the best spreads, but I can't really bothered right now to provide good ones.
Breloom: Pretty standard indeed. I'd stick way more speed EVs on this actually. If any of your mons can use a 252 / 252 / 6 spread it's Breloom actually, with attack and speed maxed and 6 in HP. Also, if you want to use a Lum Berry use it here instead of Cradily.
I'd go all out attack on Marowak. Sandstorm really doesn't provide much to Marowak and Perish Song is an amateur way of phazing, which Marowak shouldn't be doing anyway.
Marowak (F) @ Thick Club
Trait: Rock Head
EVs: 252 HP / 36 Atk / 220 Def
Impish Nature (+Def, -SAtk)
- Rock Slide
- Substitute / Focus Punch (predicting) / Brick Break / Swords Dance
I'm also thinking Adamant Nature.
Miltank looks fine, but work out it's speed. You're wasting EVs there. Set yourself a nice number which lets you outspeed some important mons, instead of maxing it out. The rest of the speed can be used elsewhere, like def or s.def.
Absol itself looks fine, but I think you need some special hitting power so I'd replace it with Starmie or something. If you want to keep Absol you could also replace Arcanine, but that is something that I would personally just never do.