AOL never merged AIM and ICQ. They may have shared some server infrastructure at times, but the networks were always kept separate. I remember as a user of ICQ prior to AOL buying them [1] there was always fear that AOL would merge the two and make it the worst, lowest common denominator of the two. For a long time it felt like ICQ had the most features of the two. (Then eventually everyone was on AIM instead. Then eventually everyone was on Google Talk instead. Then eventually everyone was texting or FB messenger or Slack or something in this modern diaspora.)

[1] I recall I had a 5-digit number at one point as a kid and switched to a 7-digit number later to appear less "weird"/elitist on ICQ.