According to this link
But that link describe the Associate Certification Path. I've not read you have to first pass 051 to attempt to pass 052...
Anyway contact your Oracle Customer Service
On the link show it says: Please Note: This is the suggested progression of the certification path. However, steps do not have to be completed in the order shown.
so that page indicates the exams can be taken in any order; but a certification will not be awarded until all the pre-requisites are met.
http://certification.oracle.com - support - faq ... I think has an authorative answer (from memory) ... but the site is currently down as I post.
However do be confident you can take the exams in any order .... however do be aware 1z0-051 then 1z0-052 should normally be the preferred order.