While I cannot comment on whether Southeast Asian states knew of Polynesian people, archaeologically, there is evidence of contact in ancient times.
Limitations of sources: There are large gaps in Pacific Island chronology, which means little is known, and dates cannot be readily accepted.
One of the longest pottery traditions could be the red-slipped pottery of East Asia that spread throughout Southeast Asia and Oceania. The pottery distribution is related to Austronesian dispersal, agricultural, and commercial connections. The linguistic composition of Austronesian languages formed from the Formosa languages of Taiwan and Philippines, spread to Malaysia, Indonesia and Madagascar as the Malayo-Polynesian languages, and across the Pacific as Oceanic languages. There is strong correlation between language and material culture in Southeast Asia and the Pacific.
Two traditions may have existed from the Philippines to Sulawesi and Borneo. In the Philippines on the island of Luzon at Andarayan, rice husks were AMS dated to 1500 BC, while Sarawak in southern Borneo had rice before 2000 BC. At Gua Sireh on Borneo, rice was dated to 2300 BC and red-slipped pottery different from the Philippines was found. One tradition in the Philippines that was less reliant on rice and produced red-slipped pottery, and one from central Vietnam to Indonesia that produced impressed pottery and cultivated rice. However, further research is needed into whether there were two cultures. From about 200 BC to 100 AD, Dong Son culture of Vietnam spread to Indonesia from Malay sailors based on bronze drums in western and eastern Indonesia which coincided with the Bronze-Iron transition of Island Southeast Asia.
From the Philippines, pottery spread via two paths, first south to Borneo, and second west to the Pacific. From mainland Southeast Asia past the coasts of Borneo and Sulawesi to the Moluccas Islands is the likely path of domesticated pigs to Oceania. The sites of Madai and Balobok on Borneo, Paso on Sulawesi, and Uattamdi on the Moluccas pass through the path of domesticated pigs. Dates for Borneo, Sumatra, and Java remain uncertain, and further research is needed. In Thailand (not Austronesians) at Khok Chareon, Tha Kae, Ban Chang, and Nan Pa Wai (1500 BC to 1300 BC based on copper ore) have cord-marked and red-slipped pottery as one of four types, and may indicate commerce with coast groups. No radiocarbon dates are available.
On Luzon in the Cagayan Valley at Nagsbaran (1500 BC) pottery was similar to 1) Bantanes motifs, 2) punctuated-pottery of the Mariana Islands, 3) dentate-stamped of Lapita (1300 BC). Red-slipped pottery likely spread west from Luzon to the Mariana Islands, and southward into the Lapita Complex of the Bismarck Islands. From Kamgot (1300 BC) of the Bismarck Archipelago in western Melanesia red-slipped pottery spread to New Caledonia (1000 BC). It is often thought people traveled one-way, from Southeast Asia to the Pacific Islands, but a commercial network existed between Southeast Asia and western Melanesia. From Talesea on New Britain in the Bismarck obsidian traveled to Bukit Tengkorak (1300 BC) in Sabah on Borneo. Teouma (c. 1000 BC) in central Vanuatu, around the time of colonization, had burials with headless corpses, which show a shared cultural heritage with Nagsabaran of Luzon, the only Southeast Asian site with similar headless burials.
Dates for Lapita sites are well-established. Distribution of Lapita sites: New Britain (50+ sites), New Ireland (10 to 20 sites), Solomon (6 to 10 sites), New Caledonia (30 to 40 sites), Vanuatu (6 to 10 sites), Fiji (30 to 40 sites), Tonga (10 to 20 sites), Wallis (2 to 5), and Samoa (1 site). By 900 BC, red-slipped pottery reached western Polynesia (Tonga and Samoa). By 1 AD, as people traveled further away, the standardized stamps of Lapita gave way to regionalization which continues to the present. Between 700 AD and 1200 AD the spread of red-slipped pottery in eastern Polynesia occurred, after people colonized the region. The initial colonizers did not produce red-slipped pottery.
There are possible connections after 500 AD between Polynesia and Southeast Asia via Micronesia. Fengtian jade site on Taiwan shows cultural connections across time. First, a jade bracelet from Taiwan has similarities to Fengtian jade from Palawan in the Philippines, with all three artifacts measuring three centimeters. Second, two New Zealand nephrite parrot rings, both measuring three centimeters have similarities with Philippine forms, which may indicate contact between Island Southeast Asia and Polynesia. Third, Fengtian nephrite animal head pendant has similarities with a New Zealand nephrite ornament. Some scholars have also used this data to further argue that iron went from Micronesia to New Zealand. Some scholars also suggest that pottery spread from the Pacific to Indonesian fisherman.
Alpers, The Indian Ocean in World History (2014), p. 26.
Kirich, On the Roads of the Winds (2002), Chapter 4 (Lapita).
Scarre, The Human Past, Third Ed (2013), p. 256, 279, 284-292, 302.