I have been reading what are conflicting posts on what staffmods are available on Barb helms, but what I think I have sorted out is that as of 1.07 (or 1.09), certain staffmods are never seen on barb helms: Frenzy, Whirlwind, double strike, beserk, and some other combat skills.

I have also heard that certain skills, like +sword mastery, only spawn on LL helms, and so never appear with +battle orders, for instance.

Is this all correct?
I have also seen some people post that it is still possible to get those mods on a barb helm, just ridiculously unlikely.

I'm trying to put Dream rw into a barb helm, and i want to know what mods I shouldn't be looking for so I can focus on skills I should be looking for in my base helm

Berserk & whirlwind very, very rarely spawn on barb helms. It uses the same complicated mess as holy shield scepters that I'm sure someone else will copy/paste in here

Obviously there were no barb helm staffmods prior to 1.07 because barb helms are an expansion item

tier 1 staffmods like claw mastery, smite, prayer, warmth only appear on low ilvl items and cannot spawn, for example, on a 6os staff or with high tier staffmods like fist of heavens or whirlwind

for your dream helm you *could* get a 3 battle orders/3 whirlwind or 3 battle orders/3 frenzy helm (and I've made one before myself) they're just very hard to find on battlenet and next to impossible on single-player (luckily they're also reasonably cheap)

What Worrywart said.

As a complement, primal helms can spawn with the following staffmods :
iLvl 1-11 : tier 1 & 2
iLvl 12-18 : tier 1 & 2 & 3
iLvl 19-24 : tier 1 & 2 & 3 & 4
iLvl 25-36 : tier 2 & 3 & 4 & 5
iLvl 37+ : tier 3 & 4 & 5 & 6

tier 1 : sword/axe/mace mastery, howl, BASH
tier 2 : find potion, leap, polearm/throwing mastery, DOUBLE SWING
tier 3 : spear mastery, taunt, shout, STUN, DOUBLE THROW
tier 4 : increased stamina, find item, iron skin, LEAP ATTACK, CONCENTRATE
tier 5 : battle cry, increased speed, battle orders, grim ward, FRENZY
tier 6 : natural resistance, war cry, battle command, WHIRLWIND, BERSERK

Bolded skills are 'attack' skills, they cannot spawn outside a procedure which gives very low chance for them to spawn.

Imbuing primal helms still gives good results at high levels, but not relevant for your concern (non magical helm for a Dream runeword).
Assuming +3 to Battle orders is desired, then you're left with a possible tiers 2 to 5 (low level helms) or 3 to 6 (high level helms).

Off-topic, I'm not aware of any good use of Dream runewords for a barbarian...

thank you for this!

I am just chasing a weird idea for a barbarian carrying as much proccing gear as possible, running around with frenzy proccing molten boulder, volcano, hydra, firewall, and so on. The confuse helps with crowd control.