Is it ethical to get participants' consent for the inclusion of their data in the research after data collection?
As long as the study is IRB approved and the approved procedures are followed, then publication should not be a problem. It seems a little strange, but reasonable, that an IRB would aprove a protocol where minimal risk data collection was kept secret, but require informed consent prior to data analysis. I would have expected consent and debriefing to happen immediately following data collection, but again, if there is a reason to delay it, that seems fine.