There's a lot of misinformation being thrown around that Ray of Frost, Disintegrate, Blizzard, and Venom Hydra cannot crit. Until yesterday I was part of this group and helped spread this false information. After reading a few posts and getting into a discussion with some friends I saw evidence that this could be wrong. Not wanting to take people's word for it I headed in-game to test this for myself.
On my current gear I have 29.5% chance to crit which I felt was enough to produce a number of crits in a reasonable amount of time (each skill I tested for 5 minutes, save for Venom Hydra which I tested for 10 minutes). I ran the experiment by swapping a 70% crit damage gem in and out of my gear, having Critical Mass, and keeping Mirror Image and Wave of Force on cooldown while attacking a group of zombies in Act 1 Inferno (ideal test subjects because they are slow). I also was sure to not use the Chaos Nexus rune with Disintegrate. I first ran my test without the green gem and recorded the the numbers I saw on my screen. Then I placed the green gem back in my weapon and quickly saw that I started getting numbers that were far larger than what I was getting before; this makes sense given that my crits were hitting 70% harder with the gem. These larger numbers also lined up with Critical Mass procs which is further proof of a critical hit. Venom Hydra is the one exception, after 10 minutes of watching it beat on zombies I saw no evidence of a critical hit.
Ray of Frost, Disintegrate, and Blizzard are capable of crits and can proc Critical Mass. However there is a bug with how the crits are shown: They appear as white text of the same size as a regular hit instead of larger yellow text like normal crits; they also do not show up on your screen if you only have "Display Critical Damage" checked in your options.
Venom Hydra cannot produce critical strikes or proc Critical Mass.