ET codeshares with SQ so chances are high that you could interline bags onto SQ at DAR even with separate tickets ... but I've never flown ET so have no experience. Good luck. Also ET is in terminal T3, as is GA while SQ is in both T3 and T2 and KL is in T1. Staying in the same terminal could be a consideration. GA has a very nice regional J, fwiw (quite a change from being an awful airline a decade ago).