Is there a dust explosion risk when shot peening Titanium 6-4 parts? Is a special dust collector required? Is there any other remediation available such as agricultural lime added to the media?

A proper dust collection system should be designed around the dust going into it. Meaning the dust must be first tested by a laboratory that specializes in testing the explosive characteristics. Such as https://www.fauske.com/ whom I've used in the past.