Lee said he never beaten Neji, this was before he knew how to use the gates; he was planning on saving it for Neji but had to use it on Gaara. Neji isn't at the level he was when Lee first used the gates, he trained for a month to improve his skills for his matches in the finals and about 5-6 weeks passed while Naruto and Jiraiya were looking for Tsunade so Neji has over 2 months of training while Lee was unable to do anything serious because of his injuries. Part 1 Neji is Neji by the end of part 1, he was able to react to Naruto's fast movements in Initial chakra cloak mode before the 5-6 weeks of training. Even with the gates Lee isn't beating Neji who can literally just rotate Lee away from him and cause Lee to burn out from the gates.
Gaara is the strongest Genin in part 1 so yes he can beat any of the genins from part 1.