The Mode C ‘veil’ does NOT apply to sUAS operations, so no need for drone pilots to worry about this.
Here is an excerpt from the Aeronautical Information Manual, page 133, for more context about how the Mode C veil applies to manned aircraft operations:
The airspace within 30 nautical miles of an airport listed in Appendix D, Section 1 of 14 CFR Part 91 (generally primary airports within Class B airspace areas), from the surface upward to 10,000 feet MSL. Unless otherwise authorized by ATC, aircraft operating within this airspace must be equipped with automatic pressure altitude reporting equipment having Mode C capability.
However, an aircraft that was not originally certificated with an engine−driven electrical system or which has not subsequently been certified with a system installed may conduct operations within a Mode C veil provided the aircraft remains outside Class A, B or C airspace; and below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport or 10,000 feet MSL, whichever is lower.