Regarding Dio's purple hermit
At the start of Series 3, according to Joseph, Stand is develope from Hamon.
When one's Hamon reach a certain level, it can create a spiritual guardian,
and Joseph call it STAND.
He relieve the word STAND from the song stand by me.

Under this explanation, I think it is pretty logical to think that Dio's purple hermit is actually developed from Jonathan's Hamon,
My personal theory is that Dio does have the purple Hermit Power but since the purple Hermit is related to Hamon, It will hurt Dio whenever he uses it,
this is why Dio never use the power of purple Hermit again. Another reason might be Purple Hermit is pretty useless against the heroes. There is no point using it.

But in a later stage, Araki explained (i think is either in Jojo agogo or 6251) that he originally want to make the World consist of all the other stand power, but he change his mind because he feels that to be able to stop time will make the World more powerful rather than to make him have all the stand's power.

Hermit Purple #2
(The italicized information below derives from a Light Novel not written by Araki. As such, it may or may not be considered canon.)

Along with activating his own Stand The World, it was stated that Dio's semi-precognitive abilities that seemed to have resulted from a Hermit Purple-like Stand were due to a Stand power that awoke in the body of Joseph's grandfather Jonathan Joestar. Similar to Hermit Purple, it can produce a psychic photograph by smashing a camera, which Dio used to track the Joestars and their friends's current location to send Stand Users after them. This Stand is also capable of showing an image present in someone's heart through a crystal ball. Dio used it to show Polnareff one image of J. Geil, as that image represented the pain Polnareff felt in his heart.

According to the JoJo novel, Over Heaven, the Stand shares the same name with Hermit Purple.

Suli619 said, April 19, 2014, 12:55:12 am

Was anybody laughing when Avdol ran away from DIO?

Yeah, a bit. But it's Avdol alright. In the Capcom game or JJBAS game he was badass.

to make matters better, david production makes the jojo females even hotter.