Not quite, for a normal bitcoin address, while the coins are stored on it only the hash of the public key is public, and the public key itself is only revealed when the coins are spent.
With a vanity address, the public key is made public as soon as the address is generated.
The hash is practically intractable, but ECDSA can be easily cracked using a quantum computer, and may possibly be susceptible to mathematical analysis.
Vanity addresses give more time for such attacks than ordinary addresses.
Since practical quantum computers don't exist yet (or perhaps "the powers that be" have one in the basement, but don't use it for fear of revealing its existence, an interesting conspiracy theory), and no mathematical attacks are known, vanity addresses are probably safe.
Only if they use the same address algorithm as bitcoin, be very careful, as if the altcoin uses the same format but a different algorithm, the coins would be burned.