Amazon removed one edition of 1984 due to it being sold by a company that did not have the copyright. Given how much backlash there was just over that, it is extremely unlikely that Amazon or any other major e-book provider will engage in any form of substantial censorship or removal of material. The risk does exist but it is so small as to not really need much attention paid to it.

A more substantial problem seems to be the great difficulty which one has in lending e-books. There have been some steps taken to handle this but they are still very suboptimal.