1 idea: avoid fighting the scarabs and attack their base right as you see them beaming your *multi-shielded* base. Multi-shields are essential for this counter-attack strategy.
You can most likely destroy a shield generator/summit or 2 b4 the Scarab makes it back. Otherwise, 50 pop of most whatever kills a base faster than a single bug can.
2nd idea: make a few vampires to explode those Ngs, killing the rest + heavily damaging the Scarab. Vampires also disable the PoR, so use some common sense.
3rd idea: make a diverse army so you can take down the Ngs, Scarabs, AND the supposeld counters. I like to use Banshees vs the Scarab/Base just circling around it, out# in Vampires for air dominance, and have Jackles for anti leader/grunts should they try to counter air with infantry...
1 more thing: you can't expect to beat 100 pop with just yourself do you? Wth is your teammate doing while the PoR's there hot dropping counters for you? The PoR's counters had better not be counters for your teammate's too?! Then you just need a smarter teammate.
I've seem this combo b4 and it wasn't a problem for me... :\
2-0 me-DC Shizface in standard 1vs1
1-0 me-DC Shizface in deathmatch 1vs1 on 2vs2 map :D