Is unit testing procedural code effective?

Question

On a current project, the powers that be want to have unit testing incorporated into our development cycle to avoid the constant amount of bugs that seem to seep into our code. The problem is that the spaghetti code is 95% percent procedural, which I've never done unit testing with (all my experience with unit testing has been with OOP code)

So my question in a nutshell is would it be wise to proceed with unit testing with our current codebase, or suggest that it be postponed until the application has been migrated to a proper OOP framework?

PS: While I tried to style this question as language agnostic, I feel that stating the application in question uses PHP and javascript will help provide more specific answers that could answer this question since from experience this occurrence occurs most with such applications.