Activating players would normally necessitate the Sabres sending players off of the roster in a corresponding move. However, according to Elliotte Friedman, a time-sensitive loophole has made it so the Sabres do not need to do this.
Quirk in Christmas rules...Buffalo can roster 24 (one over the max) since they are under the cap. Makes some teams crazy, because they feel it gives an unfair advantage, but they are not required to make a loan/demotion during Holiday Freeze
This allows the Sabres to keep extra players as long as they are salary cap compliant until after the roster freeze. This loophole has some fans up in arms about the salary cap and roster restrictions once again.
Fans Frustrated As Sabres Take Advantage Of Roster Loophole
In response to Elliotte Friedman's explanation of the situation several fans are upset that these actions are allowed.
While both of these replies seem to have sarcasm implied it still points out ways this could be exploited. The Sabres sit out of a playoff spot and are not likely to be accused of cheating.
However, if another team with more points in the standings did this there might be more complaints.