I was doing another run at Deathstrike's GC against Juhziz (God, is that all I ever talk about?!) and I noticed that when I parked a radar tank by Machine Pillbox, I saw a green beam of light shoot out to the sky.

I then saw a scud missle hit harmlessly behind my troops and I wondered if this is GLA's answer to incoming missiles, or just a special quirk of Deathstrike's Radar?

Rocksilver

I have also seen this green beam, but dismissed it as nothing.
Now you mention it, it has happened alot.

Deathstrike's Radar tank has the ability to deviate ballistic missiles, albeit to a small degree compared to the ECM Tank.

Does it also affect the Detonation range? Cause when I replayed my challenge with a camcorder on, I noticed that the explosive radius wasn't as big as a regular missile. It also seemed to fizz out the dmg, making for a lackluster threat from a usual death from above weapon of hell.

No, these weapons have a 'inner radius' and 'outer radius' where damage values are different.