although the vong could be present in the unknown region it is highly unlikly they would feature in kotor3 as in the newjedi order series it states the vong were defeated by a living planet which the jedi discover and persuade it to come back with them to stop the vong.
it is known that the vong sent scout ships past the great barior to look for bases but it had taken them a long time to establish them selves and prepare for the vongs first world ship. only one jedi knew of the vong vedrie and she kept her true identity as a jedi secret as the vong hated the jedi intensly due to their dependence and aptitude for technoligy.
although they do let on that they did have a war with a race that used technoligy and only by a being giving them the biotechnoligy did they defeat them.
alot is unknown about that region of space for all we know reven may have found a ofshoot of the sith empire or even gone their to look for lost jedi.