I wouldnt use a +25 on any of the chars that have already used +20s unless they already show a Stat cap of 250. Wait till after the recieve the +5 before you use a +25 and then yes, they should go right on up to 255.

The reason I say that using a +25 might not be a good idea is because my friend reactivated his account and got the +5 stats on all but 2 of his characters. Those characters did not get the +5 stats from AoS but had used +25 Stat Scrolls.