Ya you can use P55/Dual Channel memory on X58. You just have to keep in mind if you use more than one kit you may not, and probably not, reach the specified timings or speeds of one single kit when ran as dual channel.
Same applies with X58/Triple channel memory, it can be used in dual channel on a P55 setup as well, and in dual channel this way would likely you get better than the rated specs of the kit in dual channel than you would as rated for in triple channel.