One can only speculate if "oy vey!" was an actual source of inspiration :D
I always thought "Ho" was just a case of the special kid in the class trying to be different. It's an unnatural form of expression. Across English, French, German, Spanish, Japanese, and Hebrew, you have words like "Ah!", "Aa!", "Oh!", "Ay!", and "Oi!" These exclamations all begin with a vowel and, arguably, are entirely vowel (the "Aa" and "Ah" sound are the same; "Oh" is just "O"; "Ay" is a dipthong "Aa-ee", as is "Oi" or "Oy").
Vowels are produced with open, maximum airflow. Exclamations in this form are derived from surprise, dismay, anger, and other forms of strong emotion. Their biological basis is a warning cry, which means they begin with a form capable of providing the most power--a vowel.
"Ho" begins with a quiet, non-voiced, constrictive sound. For the expression it represents, it is completely unnatural. It's the most-likely candidate in the entire language for replacement by natural linguistic evolution rather than cross-language intermixing, and probably would have been replaced long ago if the number of native Esperanto speakers (~1,000) weren't hilariously outnumbered by academics (~2,000,000) trying to hold this ridiculous particle rigid in its pure, historic form.
Inb4 everyone starts arguing the H is silent.