Beating a Dead Horse Because I Feel Like It:
The obvious answer to the question of what \"alignment\" this \"un-aligned\" guild has is that the alignment is *towards the guild*. That is, the only constraint on the members behaviour is that it is done within guild rules and (to some degree) for guild benefit. Nebulous concepts of \"good\", \"evil\", \"law\" and \"chaos\" function as a useful standard and starting point in D&D, but don\'t wholly capture the essence of \"alignment\" to a particular cause. Some things that someone views as evil might be viewed by others as good, etc. It is only appropriate that alignments to a specific cause do not fit within the limited scope of the standard alignment framework.
To change stance and stuff the guild back into a standard alignment framework, I would say that the organization itself is Truly Neutral; not that it favours members of that alignment, but that the structure itself favours neither law nor chaos, evil nor good
(... to continue to draw this out, it could be argued that membership in a guild and conformance to rules is an indication of a non-chaotic alignment, at least in some degree... )