1.So we won't be seeing a Vivaah on a Indian Christian Wedding?
What do you mean by "Vivaaham" or "Vivaah" ? It is the sanskrit root word for wedding and in almost all Indian Languages including "Malayalam" the vernacular langauage of the Malanakara Syriac Orthodox Christians. So yes Malankara Syriac Orthodox Christians has the Holy Sacrament of "Vivaaham". But in a Orthodox Christian Vivaaham don't expect to see anything that contradicts with the Holy Bible or the faith of the fathers handed down to us from the Three Ecumenical Councils.
Can an Hindus according to Hinduism, or Hindu religions such as Hinduism, Jainism, Sikh marry a Christian or a muslim? How is that perceived from the Hindu patriotic, cultural and ethnic pov?
Anyone can marry anyone in India and the register the marriage at the local goverment registrar. India is a secular democratic republic where anyone is free to practice any faith they want and marry anyone they like.
Ethnically Malankara Syriac Orthodox Christians are Hindus. As has been clarified the term Hindu (Shindu) is a very loose term used to refer to the ethnic people living to the east of the Shindu (Indus) river. If the pagan Greek religion had survived... the practicioners of that regilion would have been called Greeks and so also would have been the Greek Orthodox Christians.
Now from a religions point of view there is not one Hindu view. Just like there is not one Christian view. For an outsider the entire spectrum starting from Seventh Day Adventists, Mormons , Pentecostals all the way to Orthodox Christians are Christians. But for someone inside the faith you know they are all different. Multiply that complexity by about 1000... and then you will get a feeling of the level of diversity in Hindu faith, culture, practices, traditions etc.
So if you ask how is it going to be percieved? The answer is.. it depends.