Can anyone confirm , will a CMMG complete RDB 9mm-Glock mag upper work on a RRA Glock mag pistol lower??

That is a blowback lower.  As was indicated in another thread it may be possible, but not without some work.

@amphibian

So isn’t the lower on a CMMG blowback?

Yeah, it is hit or miss.  
1. You will at a minimum need to remove the fixed ejector in a straight blow back lower to work with an RDB upper since the ejector will be in the bolt for a CMMG RDB Guard/Banshee or in the upper receiver for a CMMG RDB Dissent.
2.  High probability that the 'ears' of the feed ramp block will need to be trimmed down to clear the lugs of the CMMG bolt.
Picture below from my site shows an example:

3.  Lastly is where it is hit or miss in regards to the feed height.  Most Glock lowers present the mag too high for the CMMG system but there are some that work with no mods.  I have a buddy that has a cheap PSA Glock lower and all he did was #1 above and it was drop in for his CMMG RDB.  My picture above is of a New Frontier Armory S-9 (Scorpion mag lower) which also works with no mods to the mag catch to adjust the feed height.

Here is a link to my site where I detail what I did to get un-modified Colt mags to work with the CMMG RDB:
https://c3junkie.com/?page_id=374

What I didn't do yet is TIG weld a stop in the mag block to prevent over insertion of the Colt mags meaning that if you put upward pressure on the mag, it will jam.  So keep that in mind if you find that you need to lower the feed height.  You need a way to prevent that or maybe you don't care and never push up on the bottom of a mag while firing.

CMMG's Glock lower is for the RDB only....but thought you were asking about a RRA Glock lower?

Before they invented the RDB system, they sold the straight blowback Colt mag lowers (and they may still sell them..  I don't know).  They also sell a conversion kit to allow their old straight blowback Colt mag lower work with the RDB basically doing what I have mentioned above.

Not the RDB system.  CMMG also makes a blowback 9, or at least did recently.

I don't see their old straight blowback lower on their site anymore.  What is confusing is that I thought the old straight blow back lower was the Mk9.  I think they kept the name the same but if you read the product descriptions they all say they are for RDB now.
https://cmmg.com/lower-receivers
They still sell the kits to convert the old Mk9 straight blowback to RDB:
https://cmmg.com/parts-kit-mk9-9mm-radial-delayed-blowback-colt-metalform-mags
https://cmmg.com/parts-kit-mk9-9mm-radial-delayed-blowback-asc-cpd-mags

No idea if it would work for the RRA lower though

IIRC, CMMG stopped making/selling direct blowback PCC uppers (but not their direct blowback .22LR uppers) about four years ago.  Unfortunately, some product names remained the same, and obviously, customer confusion and some disgruntlement has occurred.  And there's not any really good solution to such situations for manufacturers or customers.  The 1985 New Coke fiasco is a classic example.

MHO, YMMV, etc.