I have not got either patch (2.5-SNAPSHOT or 2.5.1) to work in the way that I understood they would - that of collecting and consolidating coverage statistics across modules, so that if you have a test in module A which exercises classes in modules B and C, then the consolidated report would show classes in all three modules A, B, and C.
Currently the reports either only display classes in the same module, or display classes from other modules with 0% coverage. I accept that you can't expect to cover library classes - but these are Maven modules (as well as libraries), which are treated as 'siblings' under the umbrella of a multi-module POM project.
Maybe what is required is to produce a consolidated instrumented SER file (which does seem to happen - "consolidate-cobertura.ser" is created in the target directory of the parent project) and then drive all coverage from that, rather than individual sub-module SER files. It looks as if both patches are just running tests and generating coverage inside modules, and then consolidating.