As far as the EDM is concerned RO and ELT are NEC limited quals. As far as all other watch stations(AEA, ERLL, RT, TH, ERF, EO, ERUL, ERS, SEO, SRW, and SRO) are concerned as long, as you are a nuke, you can qualify. Yes that means as an EM you can qualify SRW, or ERS if your heart desires. As well, an MM can qualify EO and SRO, should he truly wish to put himself through it. Standing the watch however....well, that just depends on how the ship wants to handle it. I have seen 1 case of an EM being in the QWSL as RO. That however was just the Captain accidentally adding him in the RO tab instead of the SRO tab....lasted for all of 5 minutes.