As a vice admiral, Garp is fully capable of using Haki. He demonstrates proficient usage of Busoshoku Haki, being able to injure Luffy several times, bypassing his rubber body. He was also seen crushing Chinjao’s uniquely shaped head with a Haki imbued punch 30 years ago, by hardening his fist and turning it obsidian black to increase the damage inflicted. During the Battle of Marineford, he managed to punch and hurt Marco despite the latter being in his regenerative phoenix form.
Aside from his incredible mastery over Busoshoku Haki, Garp is also very knowledgeable of the other two types. Although not demonstrated to be a user of the other two types, Garp commented that Luffy has “inherited” Haoshoku Haki when it was subconsciously released (Although this may simply mean that Luffy inherited it from his father). When Coby seems to have awakened Kenbunshoku Haki on his own, Dr. Fishbonen recommended that Coby ask Garp how to master it, suggesting he has enough expertise in it to mentor others.