1. You should check your ArmA controls. Zoom in and zoom out is in the game. You find it under "View" as "Zoom in (continuous)" and "Zoom out (continuous)" I'm using dev version. For me it looks in your video like you are using the normal zoom in and zoom out command.

2. Yes I have this, too.

But because of the leaning problem you described in your video you should check the position of your TrackIR camera and the position of your clip. If you zoom in and you loose your centered position you should try to change the camera position or/and your clip position.
You should also check your TrackIR profile settings. Try it with deadzones. Maybe this helps you but also for me it isn't possible to have everything perfect because to high deadzones makes leaning uncomfortable. But saying sth. isn't working correctly while it is working as it should also isn't right.

I'm using the default Profile with a 10% deadzone with the smooth Template.
I configured Zoom In and Zoom Out correctly in the in-game controls.

The positioning of my Camera and Clip are both 100%. I have checked the camera tracking in the TrackIR software using the Camera View. Also the video I posted as evidence quite clearly shows the correct movement in the Natural Point software before I switch over to Arma3.

I am currently using the TrackClip as the TrackClipPro is on back order due to shortages and has not been delivered yet.

TrueView is ON

There is no Zoom In/Out (Continuous) In Arma 3 (you get the (continuous) notation in the corresponding TrackIR movement assigned to that binding)

This is caused by TrackIR's TrueView, it's meant for 6DOF cockpits and not for games like ArmA with independent leaning and zooming.

Turn TrueView OFF.

No, its not TrueView OFF.
I've already tested that.
Arma supports X and Z axis

My reply in the Natural Point forums:

Sorry but that's false and my video proves it.

Arma should be doing exactly what the TrackIR software is doing (exactly as demonstrated in my video)

Also, In Arma, if you press your look button (left alt) and then use your mouse to perform the same 170 degree head turn to look behind you and then press 'Zoom In' to zoom in, you zoom in, you do not zoom out.

Your statements are flawed in both respects.

I WANT to zoom in and out with my head so why on earth would i DISABLE Trueview?!?!

Heres the Natural Point bug report I submitted:
http://forum.naturalpoint.com/forum/ubbthreads.php?ubb=showflat&Number=55005#Post55005

Disabling TrueView doesn't disable X and Z axis, it just keeps each axis independent. TrackIR software doesn't have any zooming, it only has translation, so it cannot be expected to behave the same as ArmA. Make sure that you disable TrueView in the TrackIR profile that is being loaded with ArmA.

TrackIR does have 'zooming' both positive and negative. That's exaxtly what the Z axis is.

Arma2 (and I'm guessing Arma3) supports:
http://www.naturalpoint.com/trackir/03-enhanced-games/game-arma-2.html

Yaw, Pitch, X, Z

Watch my original video in the link I provided, Arma should do exactly the same as what appears in the Natural Point TrackIR configuration software, but it doesn't.

Turn head 170 degrees, move head toward screen = zoom in at 170 degrees.

Dont forget Arma is using the TrackIR SDK, not the other way around. If I can turn 170 and zoom in correctly in the Natural Point software, why can I not get the same results in Arma? Why cant Arma translate the head movements exactly the same way as the native software?

Is that REALLY too much to ask?

It is definitely possible.

The Z axis in TrackIR software does not zoom, it moves the viewpoint. The Z axis in ArmA does not move the viewpoint, it zooms. Moving the viewpoint and zooming are very different things and if you want the zoom in ArmA to always be forwards you need to disable TrueView.

Finally got it working \o/
My apologies for misunderstanding what you were trying to say.

I have created a new profile in TrackIR software, disabled TrueView and it does appear that when in a head turn I now zoom correctly.

Check the 'Exclusive' checkbox in TrackIR software to stop it from automatically loading a different profile which could be enabling TrueView.

see edited post above

I can confirm what Provenance is saying. Both zoom in and zoom out work fine independently of the players head position / rotation (using TrackIR 5 with TrueView off).

Enabling TrueView inverts the zoom direction with the head rotated beyond +/- 90°, like described above.

Here my in-game settings:
http://www.abload.de/img/arma3_trackiratk8x.png

See #0001343.