i think it depends, for the civilized people, how civilized you are. if you can survive without comforts on basic needs then you'll fare well. but yah, as a whole i think tribes would far better in general until an outbreak reached high numbers around them. it would be like nothings happening until its too late.
then they would be as helpless as the rest of us, if not more so due to our knowledge or their lack of it. i could easily see it being rumored that if you can kill one of the undead with your hands or eat a part of it you become immune to them. also other false superstitions, like amulets and magic protections. keep in mind that in some parts of africa people think if you have sex with a virgin it cures your AIDS.
in one way or another everyone has faults that could be deadly in the right circumstances. if Z-day happens it wont be cultures like tribes that survive, it'll be individuals and small groups that are either prepared or extremely lucky.
i think theres a difference between a "indigenous tribe" and a survival group. here i'll define tribe straight from wiki
"Anthropologists Morton H. Fried and Elman Service presented a system of classification for societies in all human cultures based on the evolution of social inequality and the role of the state. This system of classification contains four categories:
1. Hunter-gatherer bands, which are generally egalitarian.
2. Tribal societies in which there are some limited instances of social rank and prestige.
3. Stratified tribal societies led by chieftains.
4. Civilizations, with complex social hierarchies and organized, institutional governments.
A tribal society is thus characterized as having an intermediate amount of social stratification, more than in a mere band society, but less than in a civilization. As in the case of the Roman Republic, or later the Ashanti Empire, the transition from a tribal society to a confederacy of tribes and finally to a full-fledged urban civilization with central government is a gradual process and lacks any clear definition."
so a tribe has is generally far more complex, well established and larger the a small group of people trying to scrape out a living together. a survival group is closer to a band society http://en.wikipedia.org/wiki/Band_society without being kin most of the time (unless you hold up with your family and family friends) or being hunter-gatherers and more like scavenger-gatherers(unless your location has game to hunt).
in the end theres a pretty big differeance when you look at it.