I sure wish there was an unconventional warfare campaign being waged against north Korea. I am afraid that this "arrest" may be just part of the propaganda to counter the calls for the 6 party talks by the Chinese and demands for the north to demonstrate good faith. The regime wants to portray that the ROK and US are the threats and aggressors so that it can be the victim and force others to make concessions.
I also think that this shows the fear that the north has of religion. The religious missionaries, particularly the Christian organization can preach a "revolutionary" ideology. I think it is also important to recognize the importance that religion could plan after regime collapse when the people's ideological foundation from Juche will crumble. Religion can be very important in the people developing a new sense of identity and help to undo the 60 years of indoctrination. They will need a belief in a power higher than the Great and Dear leaders.
However, if this person did spend six years in a neighboring country conducting operations to develop internal resistance I think this illustrates the time commitment that is required to conduct unconventional warfare in a place like north Korea. It is worth doing in my opinion but it will take a long term commitment.