bigsugar: I have 7 of the 2009 model Bushnell Trophy Trail cameras. I use non rechargeable batteries as well as rechargeable batteries in them. However I do not mix them. These cameras are set up for a total of 8 AA batteries, but you can run them on four as long as you put them all in the top section or all in the lower section. Each section is wired in series, then the two sections are wired in parallel. This still gives you 6volt, but with the two sections, it is like using a larger battery. If one wanted to use both types of batteries in that camera, put 4 of one type in, say the bottom and 4 of the other type in the top. This would work because you are not mixing them in the individual section.
If cameras are bought on Ebay, there is no warranty unless the seller is an authorized dealer for the brand he is selling.
As far as voiding the warranty for using rechargeable batteries, this is the first time I heard of it, but if you don't mention it, they have no way of knowing. Sounds like they don't want to offer warranty. In that case I wouldn't buy their products.