It would depend on your definition of "Beater." While they are not specifically refereed to as "beaters," their actions and hidden ulterior motives would likely label them as such.

If you define it as Beta players who take advantage of their inside knowledge from the closed beta for their own benefit, then there are at least two.

• Diavel, attempted to manipulate a certain transaction to ensure that Kirito played a support role during the Floor 1 boss encounter, so he could get the last kill bonus
• Coper, tried to use a monster to PK Kirito, so he could get a certain quest item
• Morte, from SAO Progressive, Vol. 2, one of the Beta players that completed the "War of Elves' quest (one of three people, including Kirito), he has a hidden agenda...

Not all Beta players have ulterior motives.

• Argo, an information broker that provides the "Strategy Guide by Area", guide distributed in NPC shops, that provided many resourceful information about the game.

But all in all, the term "Beater" is just a derogatory term non-Beta players use for Beta players that don't share their knowledge and keep information to themselves. They're jealous of the knowledge they have and seek to ostracize them, so they either have no choice but to share what they know or be forced to play by themselves.

It would depend on your definition of "Beater." While they are not specifically referred to as "beaters," their actions and hidden ulterior motives would likely label them as such.

If you define it as Beta players who take advantage of their inside knowledge from the closed beta for their own benefit, then there are at least two.

• Diavel, attempted to manipulate a certain transaction to ensure that Kirito played a support role during the Floor 1 boss encounter, so he could get the last kill bonus
• Coper, tried to use a monster to PK Kirito, so that he could get a certain quest item
• Morte, from SAO Progressive, Vol. 2, one of the Beta players that completed the "War of Elves'" quest (one of three people, including Kirito), has a hidden agenda...

Not all Beta players have ulterior motives.

• Argo, an information broker that provides the "Strategy Guide by Area". The guide is distributed in NPC shops and provided many resourceful information about the game.

But all in all, the term "Beater" is just a derogatory term non-Beta players use for Beta players that don't share their knowledge and keep information to themselves. Non-Beta players are jealous of the knowledge Beta players have and seek to ostracize them, so the Beta players either have no choice but to share what they know or be forced to play by themselves.