As with all things Space Wolf, technology and the Iron Priests are surrounded by mysticism and myth. Fortunately, fielding an Iron Priest in a Space Wolves army is far more straightforward!
I can see Iron Priest being overlooked in favour of Wolfguard, Dreadnoughts, Wolf Scouts and Lone Wolves, but this doesn't mean that an Iron Priest doesn't have his uses.
An Iron Priest is essentially a Space Wolf with an extra attack in his profile, but he also comes with Runic armour (2+ save), a servo arm, a bolt pistol or bolter, a Thunder Hammer and frag n' krak grenades. He also has the Battle Smith rule that allows him to repair vehicles. So, considering his equipment, he's not bad for the points. But let's have a look at his wargear options.
0-4 Cyber Wolves - Awesome units for their points!
0-3 Thrall Servitors - Essentially Guardsmen with powerfists
Heavy Bolter for servitor - Maybe...
Multimelta for servitor - Will he be in range or live long enough to use it?
Plasma Cannon for servitor - Too expensive!
Space Marine Bike - Doesn't pair with his Servitors or Cyberwolves very well
Thunderwolf Mount - Oh hell yes!
Wolftooth Necklace - Handy if you have the points
Wolftail Talisman - If you have 5pts going spare
Saga of the Iron Wolf - If riding in a Land Raider
There are only 2 really good builds for an Iron Priest because he is not an Independant Character, therefore he cannot join units.
Iron Priest 1: 155pts
4 Cyberwolves, Thunderwolf Mount
The Iron Priest build that everyone loves! A unit of 5 Toughness 5 models with plenty of attacks. The only downside is if the Iron Priest fails an armour save. He only has 1 wound, so is instantly removed and all his pet Cyberwolves along with him. But if you can't afford Thunderwolf Cavalry in your game, this is a cheaper alternative.
Iron Priest 2: 155pts
Saga of the Iron Wolf, 3 Thrall Servitors, 4 Cyberwolves
Alternatively, you could have the Iron Priest and his minions embark in a Land Raider Crusader or a Redeemer (I favour the Redeemer) and take the fight to the enemy. This unit has 6 Strength 8 power weapon attacks (10 on the charge) and 12 basic Strength 4 attacks, so it can certainly do a lot of damage. The only downside is that you need a Land Raider to deliver them. On the brightside, with 3 Servitors in tow, the Iron Priest should be able to repair his Land Raider with relative ease!
Unlike Tech Marines of regular Space Marine Chapters, Iron Priest are not Independant Characters, so they may not join other squads of Space Wolves.
Just as well really, when Iron Priests are clearly very happy by themselves, surrounded by their creations in the Space Wolves background and in the Space Wolves army list.
Servitors aren't so hot, unless you're charging them en masse (out of a Land Raider) with the Iron Priest and Cyberwolves. That way the Cyberwolves strike first, take the brunt of any retaliation, then the Iron Priest and the Servitors clobber the enemy with their servo arms and thunder hammer. Cyberwolves are fantastic for their points though! Simply surround your Iron Priest with 4 Cyberwolves, mount him on a Thunderwolf and away you go.
The Iron Priest is a great choice in either of these roles, but because of his 1 wound, he is a little bit fragile. The same has to be said of his cybernetic servants who only have a 4+ armour save.
You can create some very characterful units, but taking basic Space Wolves packs led by a Wolf Guard is a much safer, more forgiving and generally more flexible option.
Even so, I'd still like to give these units a go at some point!
But I won't be bothering with the Iron Priest joined by 3 Gun-Servitors when Long Fangs are a far more cost effective choice.