You could maybe find a single antenna that would work, sort of. I'm thinking of one like Scott has that covers 10m ham (CB is 11m wavelength). But I don't know that they can be tuned independently. If so, there /might/ be enough adjustment to get it close for a CB. You can feed one antenna with two radios using a switch (it's called a duplexer or if there are 3 into 1 it would be a triplexer). With this you can feed one antenna with multiple radios or vice versa, one radio can talk to several antennas. If you fed a CB and a ham radio into one antenna, you could not use them both at the same time, it's either-or. I could see the benefit, one mount, one feedpoint. But even if the group I'm traveling with is mostly CB or ham, I leave the other one and monitoring anyway, so I think it's better to have two antenna systems personally. I do have my CB antenna on the ARB, it's just 4W anyway. Yeah, I don't know that they have specifically linked low power VHF with any health related issues, but I dunno that they have ruled it out either. Just like living next to high tension power lines, intuitively I know there's nothing bad about them being on the ground, I just can't get past that it might be bad. It's case where a little knowledge is more dangerous than none at all. Going through the field strength calculations in school sort of makes you think. Then you add in what the FCC and ARRL think is a biologically safe exposure and, well, you are then somewhat irrational when you have friends and family who get cancer.
