Aiming down the sights are two animations playing at once, sprinting is single animation. In GMod you can only play one animation at once.

Aiming down the sights is delta animation/animation layer. In order to create aim-down-the-sight view DOI blends this layer with idle,iron_fire and other animations. Aim<->hip (or aimed near-wall<->hip near-wall holster) transitions you see in DOI is actually blending, not compiled animation you can just play at anytime(like draw/holster/reload/firing/.. for example). Left hand that holds pistol, which you see on M1911, is part of delta_iron - animation layer.

In GMod, you can`t just play animation with this layer(if you pass name of delta to SetSequence function, gun simply rotates by 90 degrees - goes off-screen). When you play iron_fire animations in GMod, you`ll notice they have same origin as hip fire anims - gun will not center itself on the screen, so obviously you need to blend delta and firing anims. So far, I have not been able to find a way to do this in GMod. Relatively recently added http://wiki.garrysmod.com/page/BaseAnimatingOverlay seemed to be what I needed but it is not (it doesn`t apply to entity type used by CW2 for viewmodels).

Aiming in CW2 base is code that shifts viewmodel`s relative position to player`s camera, not an animation compiled into viewmodel. CW2 creates sprinting, crawling, holsters and draws the same way by default.

This is how I see the situation, if anyone happens to have experience with animation blending in GMod(on purely client-side entities) and want to help, feel free to contact me.

Since this update you can enjoy two-handed aiming with M1911 and Webley, binoculars raising before changing to overlay and more-DOI-like aimpositions on rocket launchers. The way I achieved this is compiling custom viewmodels from sources included in DOI SDK. I have simply duplicated qc entries of aiming animations and included blend anims in duplicates. This way, sweps "fake" animation blending by using animations that have blend layers pre-compiled into them. Despite satisfying results, everything said above (in Orig section) still applies.