well - they come with their own enemies - so there s no need to import enemies. when gallia pops up - its less about any factions cause to go there. - but about interests of opportunity.
many a faction has maybe an interest ( except the ideolistic factions that fight for their rights in a set enviroment - like bundschuh, unioners, xenos, rogues etc. )
some of the "global" factions like corsairs and outcasts have certainly reason to go to gallia to at least check out what they can gain there. - that doesn t mean they are welcome... both, outcasts AND corsairs would probably be shot by both, the gallia lawfuls AND the gallia unlawfuls - unless they have to offer something gallia wants. ( artifacts / cardamine )
on the other hand - gallia can itself look for opportunities ( a doorway usually opens up to both directions ) - so factions they can profit from are the BHG ( which has great knowledge about the part of sirius that was before hidden from gallia - more knowledge or different knowledge than the junkers provided ) - zoners can provide them with the same - but on a slightly different level.
gallia might even have an agreement with the LSF.. or the order if they know of the order at all. ( not sure how much informations the junkers can provide about the order - if the junkers were their main source of information )
official house forces would most probably of course NOT travel there - but diplomats and ambassadors may very well travel to and fro gallia.