From my understanding, ordinary language philosophers take it upon themselves to determine how a certain term is used in language, as a means to denote how it ought to be used. Thus, I would say that there certainly is room for discussions, but it's important to note what these discussions will be centered on.
Ordinary language philosophy tries to formally define terms based on how they are already used in languages, not come up with new semantics themselves. This means that ordinary language philosophers would argue on how exactly to turn the use of a term in common language into a more formal definition. To use Wikipedia's example of "reality," ordinary language philosophers would debate on how the word's use in common language ought to translate into some agreed upon definition and context for the word.
The idea that ordinary language philosophy does not leave much room for such argumentation would come from the fact that this philosophy does not really try to create theories for itself, unlike most other philosophies. Instead, it builds theories on existing language, and the fact that it has this foundation could lead one, as you say, to arrive at this conclusion "at first blush." However, the foundation of language is a very flexible and loosely defined one; ordinary language philosophers are tasked with determining how they ought to build their definitions and concepts upon these foundations, and so there is certainly much room for argumentation.
Therefore, the answer to your question:
Could ordinary language philosophers discuss what, for example, what terms such as "morally permissible" ought to mean?
Is: certainly, but you have to keep in mind their specific source of epistemology. All philosophers argue from their own epistemology; primarily logic, but there are also many points of difference, such as when a rationalist argues from theory while an empiricist argues from physical observations (not that the two are mutually exclusive). Ordinary language philosophers argue from the epistemology of existing language, and it is about how different philosophers perceive this language that there would be argumentation. Therefore, you could expect significant argumentation among ordinary language philosophers about what certain terms ought to mean, and you will find that they try to establish normative definitions - it's just that these definitions and arguments take their epistemology from language.
In summary, this parallelism is useful: Empiricists create normative definitions and argue about what terms ought to mean from their physical observations. Rationalists create normative definitions and argue about what terms ought to mean from their mental reasoning. Ordinary language philosophers create normative definitions and argue about what terms ought to mean from their observation of language.