They should both occupy the low frequencies.. Because a bass is a bass, and a kick is a bass drum. St least for my music style of choice, a little sidechain goes a long way. Finding a kick and a bass that doesn't sound too similar is also key, more often than not you don't want your bass to sound like your kick, or the other way around. Even with heavy sidechain it is hard to separate the sounds if they do. Layering is incredibly important. All the hard hitting kick samples you hear have been layered and processed multiple times, there's just no other way to make em sound like they do. Also it's not at all uncommon practice to layer several bass sounds together to get a rich sound out of your bass, especially in electronic music.
Oh and of course, you can't layer without EQ where it suits best.