servants having income greater than 6 lakhs are still eligible for the OBC non creamy layer certificates. They simply say that if your annual income is greater than 6 lakhs, you are not eligible for OBC noncreamy layer certificates even if your parents are group C /class III.
Revision of income criteria-The limit of annual income of Rs. 6.00 lakhs has been raised to Rs. 8.00 lakhs for determining the creamy layer among Other Backword Classes (OBCs) candidates in the centrally funded technical education institutes.
If you fall under OBC-NC (Other Backward Classes-Non Creamy Layer) category then you may apply under OBC-NC category while applying Online/Offline,even though if you have declared your birth category as GN (General) while applying for GATE. However you have to produce the OBC-NC certificate at the time of Written Test/Interview.
The eligibility criteria for admission under OBC-NC (Other Backward Classes-Non Creamy Layer) is similar to general category candidates.

Thanks,
Azim

Yes, it is valid because all you need is proof and you have that so no need to take tension of it. Although, it may cause problem if you had made obc certificate of those caste who don't come in it. Because while you submit your certificate to any purpose they check it strictly. So take care of it.

Otherwise it won't make any trouble i hope this will help you.

Good luck