Ashkenazim may take hair cuts and get married on Lagh La'Omer. This refers to the daytime and not the night of Lagh La'Omer (the Jewish day begins on the previous night). Under compelling circumstances, hair cuts and marriage may take place on the night of Lagh La'Omer. However this applies only to Ashkenazim.
Sephardim may not take hair cuts till the day of the 34th day of the 'Omer (the day after Lagh La'Omer). It is Maran z"l's opinion that weddings may not be held till that time either. However, Rabbenu Yosef Hayyim, 'a"h, mentions in Ben Ish Hai that marriages for Sephardim are permitted from the 33rd day of the 'Omer (Lagh La'Omer). In view of the fact that marriage is a Torah commandment (of Peru Urbu), it would appear appropriate to follow this custom. The weddings should not be held on the night of Lagh La'Omer, but only during the day.
Sephardim may not hold weddings from Pesah till Lagh La'Omer, not even on Rosh Hodesh Iyyar. However, from Lagh La'Omer, they are permitted to be held any day. Ashkenazim have many varying customs in this matter, and each one should follow the custom of his forefathers.
(See Maamar Mordekhai [Eliyahu], Haggim, 20:42)
Lag B'omer, Lag Ba'omer, Lagh La'Omer, Lagh Ba'Omer, weddings on the 33rd day of the 'Omer, Lad La'Omer