Luffy would have become A better martial artist and learned all rokuahiki by the time he left to be a pirate, but no, no haki. Teaching haki took a genius like rayleigh 2 years(or 1 year and 3 months to be exact) I don't think garp would have covered that much in just 3 years(grap actually rarely came to check on luffy ), I mean maybe but I personally doubt it since mastering rokushiki requires great time and dedication(sky walk and g2 speed not included, they're different techs based on the same concept)