How is the ADS-b weather derived? If the ATIS is inop, it will usually be because the sensor equipment is inop. If that is the case, how would ADS-b get the data for that airfield? If the sensors are working and the transmitter is inop, you would get the weather directly from ATC. If you were in IMC and/or IFR, your Approach plate would list an alternate source of weather info, and/or minimums adjustments when the weather is not available.
Saying that, having the weather is not a requirement to land at a Class G or E airport in VMC. Most airports will revert to one of these when the tower closes. A pressure sensitive altimeter is not necessary in VMC. Title 14 CFR, Part 91.205(b) just says “Altimeter”.
In all other cases, follow the regs below:
91.121 Altimeter settings
(a) Each person operating an aircraft shall maintain the cruising altitude or flight level of that aircraft, as the case may be, by reference to an altimeter that is set, when operating—
(1) Below 18,000 feet MSL, to—
(i) The current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft;
(ii) If there is no station within the area prescribed in paragraph (a)(1)(i) of this section, the current reported altimeter setting of an appropriate available station; or
(iii) In the case of an aircraft not equipped with a radio, the elevation of the departure airport or an appropriate altimeter setting available before departure; or.
(2) At or above 18,000 feet MSL, to 29.92” Hg.