The proofreader's part comes after the translation. It's registration and management by translation manager are roughly equivalent to translator registration and translator management, except they are monolingual, i.e. the proofreader just has to work in his/her natural language.
Of course, translators can be proofreaders, and the other way round. It always help if proofreaders can read the original text, in order to evaluate the translation better.
However, in many cases the proofreader will be chosen because of his/her expertise in a specific field, most translators being generalists.
Usually, translation processes reaching certain quality standards include proofreading. Translations are often imperfect as such. Either the translator didn't know the subject quite well, or had no time to proofread, or whatever. Therefor the translation manager should be able to set if proofreading is necessary for a precise translation unit or for a precise translator as part of translator management. In websites with few translation managers available, Admin should be able to check or uncheck a generic proofreading obligation.
In an advanced multilingual cms, the proofreader can become an essential part in the feedback phase of the translation process.