All Nod stealth vehicles are detected by primary Def (AGT), even by some secondary def (Comanche is detected by the capturable Flak, Def built by pioneers also shoots Nod stealth units).
The important difference is: It is not possible to plant automated defense against spies, also the default def (obelisk,...) is useless: the smaller a Nod-team is, the more OP spies are. In vanilla Renegade, this has never been possible for units you can simply buy. And expensive is no argument here, at maps with refinary both teams have more money than they can spend.
In original C&C, spies could be countered automated with guard dogs. Even MSAs don't lead to spies getting shot by defense.
Allowing such an OP infiltrator to plant beacons or building-killing explosives results in the most OP unit ever seen in this game - the 1400creds Nod SSM heatseeking orcas was a joke against this.
And mines aren't a sufficient countermeasure because you don't have to plant beacons in buildings.
Speaking of OP units: The current SIDAM kills more expensive dedicated anti-tank vehicles in 1 on 1 encounters.