While I understand the community frustration around working with companies with less than exceptional employee records, my main concern with sponsors is, as always, if the content is misleading.
If LTT was sponsored to walk around a DC and show everyone's (forced) smiling faces, that would be one thing: however, if you were using the sponsorship as a vehicle to show off cool tech or facilitate other interesting content (like IETU), I don't think there is any problem with it.
If a consumer chooses to use Amazon as a result of the sponsorship, they will be treated well by their service/support (at least in my experience), so promoting them doesn't seem to come into conflict with the ethical standards that LTT has previously established.