I'm keen to start DBS RSP for STI ETF. Are there guaranteed dividends on the ETFs?

Please avoid STI index as a vehicle for ETF investing, when there's much better performing, historically proven index out there such as the S&P 500.

Buying an index ETF is akin to buying a basket of companies, so if most of these companies paid out a dividend, yes you will received it. But how much dividends is going to be paid off is never guaranteed.