Uriah was the one who nailed it on the head. Any music professor will tell you that reading is a part of theory. So is ear training. They both are minor subjects that make up the larger concept of theory. When "Gospel" people think of theory they mostly thing of scales and modes but that's only one part of theory training. If you go to
www.cyberfretbass.com you will see that when you say theory you're talking about several subjects.
Yes everyone should learn to read or at a minimum be able to identify key signatures because for us bassist, once we know the key signatures, it's just a matter of hand placement because once you place the your hand in the correct position then all the notes for that particular scale should be under your fingers.
Theory bassed on Godsbassman's definition may not be important because some kats have dynamic ears. Here's the problem with having great ear without any theory training. 1. You can't teach effectively. If you have to explain to another bassist what you did who is seasoned or even a new player, you just say "Play it like this." 2. Your ability to communicate with other musicians specifically trained musicians especially keyboardist, it limited. Leads to more confusion. 3. You ability to be creative during improv is limited because part of theory teaches you how to play the notes that sound good or match the progression that you make in a song.
The answer is balance: If you really want to be good, learn all of it. If you think of scales as theory than it is important. It will give you lines more definition.
My two cents...