Are haircuts permitted on lag beomer for those keeping the second half of sefira? Did some research and cant find an answer.
Rama OC 493:3
בהרבה מקומות נוהגים להסתפר עד ראש חדש אייר, ואותן לא יספרו מל"ג בעומר ואילך, אעפ"י שמותר להסתפר בל"ג בעומר בעצמו. ואותן מקומות שנוהגין להסתפר מל"ג בעומר ואילך, לא יסתפרו כלל אחר פסח עד ל"ג בעומר
In many places they are accustomed to take a haircut until Rosh Chodesh Iyar, and they shouldn't take a haircut from Lag BaOmer on, even though it is permitted take a haircut on Lag BaOmer itself. And those places that are accustomed to take a haircut from Lag BaOmer on should not take a haircut at all after Pesach until Lag BaOmer.
As sam points out, for Eastern Ashkenazim (ie. non-Yekke) who are keeping the "second half", some say (see Beer Heitiv ibid.) that haircuts can be taken even in the afternoon leading into Lag BaOmer and there is no need to wait for the morning. In my experience this opinion isn't commonly practiced.
Cutting hair after lag bomer Rabbi David Sperling from Yeshiva University states that Ashkenazim can cut their hair during the day of lag baomer but not the previous night.
Others, however, start their semi-mourning from Rosh Chodesh Iyar and continue it until 3 days before the festival of Shavu'ot. (There is a variation on this custom that counts from the 2nd day of Rosh Chodesh until the day before Shavu'ot). According to this tradition, one would not cut their hair after Lag B'Omer. The Ashkenazim who hold according to this opinion may cut their hair on Lag B'Omer itself (in the daytime) but not the days after - until reaching the days before Shavu'ot.