if i had an a range g2 transmission
could i pick it up with an a range g3 receiver
yes
compatible like this ?
he thinks yes but his yes not enough.
All evolution is compatible with all evolution - G1, G2, G3, 2000 series are all compatible with each other.
As the switching bandwidth gets larger as you go on (24MHz with G1, 36MHz with G2, 42MHz with G3 and 75MHz with 2000 series) you need to make sure that the frequency you want is available on both units.
Also - if you use a G1 transmitter you will have to switch off the pilot on the G3, G3, 2000 receiver to hear it.
So - yes - it will work fine.