A 50mm tire might be straining the upper boundary, but I'm not certain. I can't find an inner bead spec for the CR18, but the Equalizer 21 is 1.5mm narrower and has an inner bead of 16mm. Following suit, the CR18 is probably a 17 - 18mm inner bead measurement, which puts you at a 42mm tire according to the Sheldon Brown Tire Sizing Guide. However, it's been shown that Sheldon's charts run on the highly conservative side. For instance, I have a 32mm tire (true measure of 30.6mm) on a DT RR1.1 rim which measures 14mm internally. I've used a 35mm studded tire (true measure 37.5mm) on the same rim without any problems.
There's a guy in my rando club using a 20mm outer width rim and a 42mm tire with no problems. Looking at the specs for other 29er rims on the Sun-Ringle site, many measure up at 23 - 24mm So, you might not have any issues with a 50mm tire on the 22.5mm CR18.