Almost any skill/ability, except orb effects, are stackable as long as they have different buff.
Evasions stack diminishly, which means that a chance to proc the another evasion is checked first, then the another.
As I said, they stack as long as they give different buffs. Please check your information before accusing other people for misleading.
Critical strikes will have individual chances to proc, so sometimes the 20% 2x will come out, while the 30% 3x will come out other times. If both proc at the same time only the last acquired multiplier will apply, even if it's lower, but the number shown will be 6x in this example and will be incorrect.