I've never once seen a dodge cause a change in attacking on my powertech. I usually run close to 20% defense on him when I tank.
Also, gut is bad for tanking. Don't use it. Get energy blast instead.
As for the powertech I will admit I've only 2 characters (vanguard and sage) so I don't know what it's like playing other characters.
About gut, I'll be honest in that I like it, I've been reading about how it's horrible for vanguard tanks and Energy Blast is better. I personally haven't decided. On paper Gut should do more damage because of the dot, and the main reason I went with it originally was because it was there next to Frontline Defense, which I found extremely useful in flashpoints and PvP. I run without Energy blast and seem to do fine in HM EV/KP and I've also tanked most of HM TFB (group split up when we got to the tentacles because one of the healers was too pissed off with the other tank). Again I'm not saying I know everything, I did try Energy Blast at one point and found I didn't really like it much, but ammunition management was a lot better with Energy Blast than it is with Gut. I will admit maintaining the screens is a little easier with Energy Blast, but I feel like I get by okay.