They certainly did feared that but in practice that happened only once, but usually they didn't even feared that much, as evidenced by them routinely arming helots in large numbers to use as slingers/peltasts screen for their hoplites, and those helots never once rebelled in the army. Spartans had interesting methods of controlling them though, mostly through secret police (krypteia, the killing ritual described in sources is almost certainly fake though, there's no other proof for it and it would caused rebellions like every two years) and in at least one case they took the rebellious helots, armed them (as hoplites! expensive as fuck!) and send them to conquer some other city, which was successful.

Thing about Spartan history though, which is very relevant for the current historiographers, is that basically no other state in antiquity is so propagandised. Basically everything we know about them was either from Xenophon who was incredible spartaboo and passed a lot of both praise and terror propaganda as truth, and from Roman era propaganda which was mostly fabricated for tourists (Sparta was first literal tourist power in history) and as such filled with 150% militarised heroic stories.

There are also material evidence that cult of mythical Sparta was already in motion just few years after Sparta was defeated by Thebes, even Theban soldiers copied Spartan aesthetics.