Will my results still be publishable if I used ethically objectionable techniques in my research
All research involving EEG on human subjects will require IRB, or equivalent ethical review board, approval in order to be published in a reputable journal. Studies involving pornography, violence, and death are not that uncommon and your IRB will have procedures in place to deal with these types of studies. They will likely require you to provide clear information about what the subjects will see during the experiment if it does not impact your hypothesis. They may require you to prescreen subjects for past experiences that may make the images more salient, again if it doesn't interfere with the hypothesis. Finally, if the images are disturbing, they will likely require you to have a support mechanism included in your debrief. Often, if the subjects are limited to students, understanding how to get emergency access to a psychologist is enough. In extreme cases they may require a psychologist to be on site.

NEVER do research without ethical approval. There is nothing in your proposal that sounds so shocking that it should cause a supervisor to think less of you. He/she may not want to go down that road on scientific or personal moral grounds, but you should still feel comfortable raising the idea with your supervisor.