The catch can is completely separate and yet still related to the EGR mod.
Separate: the EGR mod won't increase the amount of blow-by significantly just like it doesn't increase the engine temperatures significantly. Yes there is a sight rise, but in the greater scheme of things it isn't large enough to be of any concern. The catch can is there to catch oil vapour in the blow-by before it is fed to the intake manifold, removing this oil from the combustion process.
Related: Both EGR and the PCV system introduce exhaust gases into the intake manifold. Both dampen combustion.
The catch can isn't a bad mod. I'm in the middle of fitting mine right at the moment, and will have that finished tomorrow, along with a fully sealed air box.