The Indonesian men were detained on Friday by the Vietnam Coast Guard for their part in the incident involving the 7,301-dwt Orkim Harmony (built 2009).
The Vietnamese also seized the boat that the suspects were in, which is reportedly the life boat of the Orkim Harmony.
Reports say the suspects claimed that they had come ashore after their fishing vessel had sunk. Vietnamese authorities say their investigation is ongoing.
News of the arrests has come from Singapore-based Regional Cooperation Agreement on Combating Piracy and Armed Robbery against Ships in Asia (ReCAAP) Information Sharing Centre.
Earlier on Friday it had emerged that the perpetrators behind the Orkim Harmony attack had abandoned the vessel and that it was on the way back to Kuantan in Malaysia.
On Thursday Malaysian authorities had said they were shadowing the vessel and were trying to persuade the hijackers to surrender.
State news agency Bernama, quoting Malaysia's naval chief Admiral Abdul Aziz Jaafar, said the pirates had repainted the ship and changed the name to Kim Harmon.
The Malaysian-flagged Orkim Harmony lost communication with its owners in early June.
The ship was reportedly carrying 5,879t of RON95 fuel worth MYR 21m ($5.5m) which belongs to state-owned oil company Petronas.
The ship also had a crew of 22 people made up of Indonesians, Malaysians and Myanmar nationals.
It was the second Orkim Ship Management-controlled vessel to have been attacked by pirates in the space of eight days.
The 7,119-dwt Orkim Victory (built 2009) was hijacked and had its cargo of fuel siphoned off and stolen in the early hours of 4 June 2015.
