They have been observed by astronauts according to this paper and ESA. Both articles do not make a note on wether the astronauts could see the TLEs without aid.
The second article also mentions the ASIM, which is a dedicated sensor to permanently look out for this phenomena. It is planned to launch in 2018 on a Falcon 9.
Red sprites can be observed with the naked eye, blue jets are very short-lived and are unlikely to be seen without aid according to this. However, like in the other sources, no mention of an unaided sighting.
This work does mention sightings by pilots. It can reasonably be assumed, they where unaided:
Vaughan, O. H., and B. Vonnegut, Recent observations of lightning discharges from the top of a thundercloud into the clear air above, J. Geophys. Res., 94(D11), 13,179-12,182, 1989.