Looking at the top 5 seeds at the chesapeake regional, it doesn't look like the parter assignments are rigged. Since the team number is a pretty good indication of the amount of time a team has been in FIRST, I simply averaged the team numbers of each of the top 5 seeds parters and opponents
Code:
Rank Team # Average Partner Average Opponent
1. 222 488 694
2. 1405 868 749
3. 1083 708 733
4. 25 645 777
5. 303 486 760
If anything, the two newest teams had worse partners and better opponents then the 3 teams that had been around for more the 5 years.
Obviously, this is a very small sample. It would be better to do it on a smaller regional, where there are more matches to average out the differences.