I just realized that EA has been running a "Five on Friday" Q&A feature on the official Ultima Online website. In this week's installment, answers are given for questions pertaining to the Virtue Armor set, the duration of Cursed Weapon, and more.
Q: Does being in party affect the 10th Anniversary Event artifact drop rate?
A: Actually being in a party does not affect the drops or the points given out out all. However, if multiple people are fighting the same creature - whether or not they're in a party - that does affect the rate of points given out.
To get points, everyone must make the top attackers list. (The top attackers list is simply the top 16 damagers.) So you can't party up then let someone else do all the work, and still get credit.
Next, points are scaled based on where you are on the top attackers list. The overall highest damager will get the same amount of points he would when soloing - everyone else will get increasingly smaller amounts, down to about 1/7 of the usual if there are more than 12 attackers on the list.
So while fighting with two or three people could be much more efficient in terms of kills per hour, and therefore total points, having a full group may be less efficient for the people who tend to do less damage. On the other hand, if you want to take your crafter out to do some hunting, pair him up with a fighter and make sure he smacks each critter at least once, and he will get some credit for the kill.