The eligibilty criteria present on the website talks nothing aboutrequired percentages in the senior secondary level. Also it does not talk about whether it is compulsory to pass in all subjects or not. Hence it would be safe to assume that they would consider your present engineering degree only for appearing in the exam.

As far as PSUs are concerned, all of them have their interviews (this is true for academic institutions also).So they might or might not object to your score in Class 12th. You can appear for supplemantary exam and clear your back in maths just to be safe.