They call it a “Vedic” chart, but actually its an “Indian” chart, unless you want to believe that anything Indian is automatically “Vedic.” We have no record in the Veda of ANY birth charts at all. “Veda” particularly means Ṛg, Sama, Yajur, and Atharva, but can also include the Upaniṣads and the Purāṇas. There are a lot of books about astrology written in Sanskrit, but they are not part of any of the above groups. They are written from 1300 AD onward. Brhat Parashara Hora Sastra makes a brief claim to being very, very old, but so do most books written in Sanskrit. In any case everyone knows that the BPHS we have today was assembled only 2 centuries ago after being lost for a very long time. The point is that no authentic Vedic texts state specifically how to use astrology in a natal manner for casting individual charts, So there is nothing but bravado in the claim that someone is a “Vedic astrologer” or practices “Vedic astrology.” An honest person would say they do “Indian astrology.”
An Indian chart tends to use sidereal zodiac measurements – but the irony is that this contradicts the definitions of the zodiac very clearly and directly given in authentic Vedic texts like Bhāgavata Purāṇa, and in very respected Sanskrit astronomical texts like Sūrya Siddhānta. For more information on this, you can see my video and article on http://www.vicdicara.com/rashi
I have to say that there is a lot more to astrology than merely the zodiac, but still those who claim that a chart cast in Tropical zodiac coordinates cannot be considered “Vedic / Indian” are simply delusional.