1.005 is barely considered brackish... typical SW is 1.023.. most brackish is considered in the 1.012 rangeish.... while they are sometimes found in these water perameters i've yet to find any credible evidance it's "required" or ideal. btw.. the picture in the link is an M. Dayii.. not an Armatus as they lead you to believe, 'nore even mentioned. but not horrible generalized info.I have not had issues with feeding them in reguards to being shy once live worms are offered. in all 3 set-ups that hold spineys each species is quite aggressive feeders and will chase off other fish to get their share.
reguardless of if you decide ot keep them in brackish or not, they should never be mixed with puffers or aggressive fish, being scaless a minor abraison can quickly become a major infection. imo the only FW eel suitable for brackishs etups are G Tiles.. a true moray that will need full marine once mature as a majority of brackish fish need.
a full stock list would be beneficial to say weather its even worth a try.. though i wouldn't personally do it.
I have kept fire eels in low end brackish successfully for years, alongside morays. I would characterize 1.005, like my tank, as low end brackish, but not "barely". Most FW fish and almost all plants die at this salinity, but there are many "Brackish" fish that do best there.