...because there was a question concerning the repeatability in zeroing the weapon and the stability of the optic. Yet, Figure 2-26 in the Army Rifle Marksmanship manual (FM 3-22.9) shows an Aimpoint mounted on a RAS II in combo with an NV scope. (www.adtdl.army.mil/cgi-bin/atdl.dll/fm/3-22.9/c02.htm#2_2)
Can somebody clarify this for me?

What you are seeing and reading in that manual is the Knight's RAS, not the RAS II. The RAS II is the one with a bridge connecting it to the receiver. RAS II free floats the barrel and is plenty stable to support and return to zero optics.
The RAS, well, the manual you have there says it's stable enough. You will have plenty off people telling you that they have mounted optics on the RAS with no zeroing problems.

Other people will tell you it's not a good idea, as the RAS doesn't free float the barrel and the unit could flex the barrel because of it.
I personally have both units. While I wouldn't mount an optic on the RAS because IN THEORY it could flex some, it does appear to be very stable and as stated, others have done it without any problems. Thanks.....Chad

Even if the M4 or M5 RAS moves a little if it heats up during extended firing, the fact that you are sighting with a 4 MOA Red Dot through the M68 (Aimpoint) combined with the natural randum dispersion of issue M855 ammo at a man-size target at less than 200 meters completely mitigates any "error" that can be measured as a result of rail movement.
Mount your Aimpoint to the top rail where it suits your eye relief/shooting needs and dare anyone to stand out in front of you at 200 to prove you wrong.

Thanks for the insight. I am trying to wait for ARMS to come out with a rifle-length SIR# 51, but if that doesn't happen, then I will opt for a RAS.