Do engineering colleges have uniforms for B.Tech courses?

It depends, but let me tell you that formals are a must for all the top universities if you want good placements. Some universities have certain days to wear formals. If any university/institute does not have formals or dress code, then you can understand their placements also.

It depends upon the institute itself. Like some institutes have dress code or uniform for their students and some institutes does not have any restrictions, uniform at all. However, for some special subjects you have to wear uniform like: 1) During chemistry lab experiments you have wear a lab coat.