Sure. They're both 2x clocks so they'll be edge-aligned(and Quartus will analyze any delay differences). Where it doesn't work is if you create a slower clock, such as a 1/2x clock, or 25MHz clock, with the two PLLs. There is no guarantee that theyir generated clock will be aligned, i.e. half the time the rising edge of one will correspond with the falling edge of another.
