well there are guys that have multiple account for tourneys to enlarge their changes to cash big - also seen such a "drama" on the pro's on FullTilt and was really funny to see that such pro's make such stupid mistakes
it is just one acc per person allowed and usually they take their husband or any other family member for another account
so if they are playin in the same event and they are colluding, they will most surely caught, at first they got the complete history saved on the sites and also check the IP
as for you, you dont need 2 accounts, stick to sessions with cashgame and when u get bored just play sit n go - easy way to find out where u make more cash and for each session u can track ur results - there are a few converting tools like pokertracker etc so u dont even need to make notes urself, the program will do that for you