I believe that Ochem is a universal requirement for Dental schools while Biochem is only required for a handful of school. Substituting Biochem for Ochem is going to be a rare exception of at all. Plus I would recommend that you take both anyways to challenge your self and boost your resume by showing some depth in your courcework. Dental applications are getting very competetive, so just completing the 'requirements' really don't cut it anymore. GL
and besides the whole cutting corners thing that was mentioned above me, I'd also like to point out that much of the orgo on the DAT is from the second semester Organic Chem. So if you are planning on taking the DAT anytime soon, you'll want to have that knowledge too. My DAT had alot on benzene reactions and IR spec that is taught in the second semester.
Plus, every school I applied to required 2 semesters of orgo. Just suck it up and take it. I think it was easier than first semester orgo and it really helped since i scored a 28 on the orgo section of the DAT.