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Is accepting a Law PhD without legal practice first a detriment to being able to 1) practice as a practitioner or 2) work as an academic in the future?

Do you mean an SJD/JSD, or an actual PhD? A "PhD in Law" doesn't really exist--the equivalent degree is the SJD/JSD. Either way, mostly irrelevant for academia (most legal academics have only a JD, with SJD/JSDs being strictly optional, but PhDs in related fields, like economics, business or political science, may be considered helpful) but probably damaging for legal practice (except for a science PhD for a patent attorney) simply because of the mostly wasted time investment and perception of being a flight risk to academia or another field.

Not sure why anyone would want it, but http://www.law.yale.edu/graduate/PHD_program.htm .