I read somewhere that Varaha has one tusk instead of two. Is that true?
Yes, Lord Varaha have single tusk as per Valmiki Ramayana: Yuddha Kanda: Sarga 117
भवान्नारायणो देवः श्रीमांश्चक्रायुधः प्रभुः || ६-११७-१३
एकशृङ्गो वराहस्त्वं भूतभव्यसपत्नजित् |
"You are the Lord Narayana himself the glorious god, who wields the discus. You are the Divine Boar with a single tusk, the conqueror of your past and future enemies."