It sounds like you want to use an alternate noise reduction algorithm integrated into Lightroom's RAW conversion, as an alternate for or addition to the built-in noise reduction.
I don't think there are any plugins that work that way. Everything I can find uses Lightroom's external editing functionality — which sends a processed TIFF or JPEG to the other application. (See for example the instructions for Topaz Labs.)
The program Photo Ninja, which can operate as either a stand-alone program or a RAW converter, apparently has some workarounds where it will match up previous settings to the linked file. That might be Good Enough for your workflow, depending on what you want.
The other good news is that Lightroom's internal noise reduction functionality is quite good. Make sure you master that first and are sure you'll benefit from an external piece of software.