Can a professor from totally different research field be invited to thesis defense?
I'm not familiar with UGC policy. However, in the UK university I'm in, this would be considered a serious breach of protocol and may be grounds for invalidating the viva and its result.

The attendees at the viva are limited to four people: 


An internal examiner
An external examiner
An independent observer
The PhD candidate


The qualifications of the first three have to be vetted by the Department, Faculty and Graduate School. The independent observer is a senior professor of my university who is not necessarily in the cognate discipline. His or her role is to ensure that the processes being followed meet university standards.

The proceedings are held in one of three special rooms we've designed for the purpose of the viva. The proceedings are not audio- or video-recorded. (We do allow the taking of photos of the attendees at the end of the proceedings.)

I can understand the idea of nominating local experts to reduce costs. However, the vetting process specifically seeks information about (1) conflicts of interest between or among examiners, supervisors and students and (2) the qualifications of the internal and external examiners to hold those positions.

I hope this helps.