I've seen some of the other takes on Ogryns, most of them originally made with Dark Heresy character creation in mind, and I figured I'd try to put something together that's a tighter fit with the Rogue Trader character creation rules.
To do this, I've added Ogryn as a new choice under the Tainted entry if - and only if - the character hails from a Death World. Additionally, the player must spend 500 xp to select and play an Ogryn character, and the character's starting Fate Points are reduced by 1. An Ogryn is treated as a Mutant with the Brute, Feels No Pain, Hideous Strength, Hulking, Mental Regressive, and Tough Hide mutations. The effects of these mutations can be found on page 369 of the Rogue Trader Core Rulebook.
An Ogryn character may elect to undergo an augmentative chemical process called Biochemical Ogryn Neural Enhancement (BONE) as a Very Rare Acquisition (for Common Craftsmanship). BONE reduces the effects of the Mental Regressive mutation in an Ogryn (but not in other unfortunates with this mutation). When determining the effects of the Mental Regressive mutation on an Ogryn with BONE, treat results of 6-7 as if a result of 1-5 had been rolled and treat a result of 10 as if a result of 8-9 had been rolled. In addition to these effects, a Good Craftsmanship BONE changes any Characteristic reductions from the Mental Regressive mutation from 1d10 to 1d5 and also reduces the Insanity Points caused from this mutation from 1d10 to 1d5.
That's the basics. It's certainly physically powerful, but also somewhat limited. The initial buy-in costs of 500 xp and 1 Fate Point (and quite likely the character's free starting Acquisition too) helps to balance the nice mutation benefits. Remember that Hulking provides a bonus to BS tests made to target the Ogryn as well as a penalty to Concealment, so there's a bit of a negative factor here too.