yes you can appear for BITSAT without appearing for jee main but both have the same syllabus and almost same quesion pattern. In BITSAT you have extra syllabus with english and reasoning part

hence its advisable to prepare for jee main so that remaining competitive exams can cleared easily

all the best

hello uttam,

yes, you can appear in BITSAT exam without appearing JJE main exam.

Candidates need to have passed their 10+2 or equivalent exam from a recognized Central or State board or its equivalent with Physics, Chemistry, and Mathematics as subjects and adequate proficiency in English.

there are required 75% aggregate in PCM.

read here the full article of eligibility criteria for BITSAT exam 

https://engineering.careers360.com/articles/bitsat-eligibility-criteria

good luck.