We see that Rakshas are non-Vedic people but in case of Ravana, he is a devotee of Shiva. Daityas are non-Vedic but in case of Bali, he is said to have performed 99 Yagyas with his Purohit Shukracharya. The Yakshas are non-Vedic but in case of Kubera, he is worshipped as a lord of wealth.The Gandharvas and Apsaras are also seen to be in close relation with the Vedic people. The Kirata, Kimpurusha, Kinnara lived adjacent to Vedic kingdoms and in the Himalayas but not much is mentioned about them.
The Danavas and Daityas ,although belonging to the Asura group, we find that martial relations were established signifying intermixing to some extent.
The style of marriages also seem to be influenced by different communities. Let's see the 8 types of marriages in Hindu customs-
- Brahma Vivaha - Where the parents of the bride and groom decide the marriage and with the consent of all.
- Prajapatya Vivaha - Where the bride and the groom are married off at a young age. The responsibility of the bride lies on the groom's father and not on the groom himself till both of them attain the right age. Prajapati directly means one who takes care, Possibly that's why this type is called Prajapatya since the father takes are of the bride.
- Daiva Vivaha - Where the bride is poor and her marriage is performed as a charity by rich people.
- Arsha Vivaha - This type is applicable for those communities where the groom has to pay an oblation to the bride to get her.
- Asura Vivaha - Where the bride is not suitable for the groom but still they marry. Asura communities seem to have such type of marriages.
- Gandharva Vivaha - This is proper love marriage where the consent of parents is not necessary. Gandharvas and Apsaras used to marry the person of their choice.
- Rakshas Vivaha - This type involves abduction of the bride if she is ready for marriage. The Rakshas tribes used to marry in this way.
- Paishacha Vivaha - The bride is intoxicated and is not in her senses while marrying. That's why it was called Paishacha vivaha on the name of Pishacha.
- Pururavas Aila and Urvashi - Pururavas was a Chandravanshi king. Urvashi bore 6 sons from him.
- Prachetas and Pramlocha - Soma was the son of Atri. His adoptive daughter was Pramlocha who was married to Prachetas, a descendant of Dhruva.
- Trinavindu and Alambusha - Trinavindu was the king of Vaishali kingdom and a Chakravarti Samrat
- Agnidhra and Purvachitti - Agnidhra was the grandson of Swayambhuva Manu.
- Raudrashva and Ghrutachi - Raudrashva was a king in the Puru dynasty of Hastinapur.
- Vishwamitra and Menaka - Although they didn't marry, they bore a daughter Shakuntala who married Dushyanta. Their marriage took place by Gandharva Vivaha.
- Ruru and Pramadvara - He was a rishi. Pramadvara was daughter of Vishvavasu Gandharva and was brought up by Sthulakesha rishi.
- Vatsaka and Mishrakeshi - Vatsaka was a Yadava prince.
- Rucheyu and Jwala - Rucheyu was the son of Raudrashva, the Puru king. Jwala belonged to the Takshaka tribe of Nagas.
- Arjuna and Ulupi - This couple is quite well known from Mahabharata.
- Shantanu and Satyavati - Shantanu was the great grandfather of Pandavas and Satyavati was Vyasa's mother.
- Yadu and Dhumavarna's daughters - Yadu was the son of Yayati and Dhumavarna was one of the Nagas who married his 5 daughters to Yadu.
- Purukutsa and Narmada - Purukutsa was an Ikshavku king. Son of Mandhata.
- Kusha and Kumudvati - Kusha was Rama's son.
- Somashrava - He was a disciple of rishi Yajnavalkya. His mother was Naga princess and father was Shrutashrava rishi.
- Yayati and Sharmishtha - Sharmishtha was the daughter of Vrishaparva Daitya.
- Yayati and Devayani- Devayani was the daughter of Shukracharya, the priest of Danavas and Daityas
- Vishrava and Kaikesi - Vishrava was a descendant of Pulastya and father of Ravana. Kaikesi was daughter of Sumali Rakshas.
- Bhima and Hidimba - Hidimba was a Rakshasi who met the Pandavas after they fled the Lakshagriha in Varnavati. Ghatotkacha was their son.
But strangely, we don't find any Vedic princess being married to a non-Vedic groom.
From this, we can conclude that the ancient people were not that averse in marrying with non-Vedic tribes. Although the names given above are less, at least we can establish that Vedic kingdoms had alliances with these non-Vedic tribes and kingdoms which had the capacity of influencing the politics of the land. In the case of Arjuna and Ulupi, the Naga kingdom to which she belonged supported the Pandavas during the Mahabharata war. Similar was the case with the Rakshas tribes who supported the Pandavas because of Hidimba and Ghatotkacha.