Is 98%+ purity Reagent Grade Ca-EDTA powder as safe to use as USP Grade in the body?
While normally health-related questions such as this one are considered off-topic, this one is sufficiently cut-and-dried that it probably merits an answer.

NO!!!! In general, reagent-grade chemicals are NOT safe to use internally like USP grades.  The entire point of the USP specifications is to ensure, to the extent practical, that the relevant chemicals are prepared from suitable starting materials and using suitable methods such that toxic or hazardous materials are absent from the final product. This is a big reason why the USP grades are often more expensive than the lab grades.

It's certainly possible that a given reagent-grade chemical may actually be safe to ingest, but there is no real way to know for sure without conducting extensive analysis of the impurities.