Are vanity addresses Vanitygen generated really safe to use? I’m not talking about whether Vanitygen can crack an any existing wallet or not. I know it is practically impossible, considering the computational resources required.

But what if, it’s to crack vanity addresses generated by itself, Vanitygen?
If Vanitygen is deterministic and does not take any input (such as a seed) other than the desired pattern, in other words, does not walk along random steps, given the pattern input is the same, it would always require the same amount of computational resources to generate the identical first match, which is mostly affordable.
Do Vanitygen have some kind of countermeasures for this problem? Is it safe to use Vanitygen-generated wallets, free of the threat of Vanitygen-regen?
The key point here is that vanitygen is not deterministic - It relies on entropy provided by the system it is running on, which is why running it multiple times with the same pattern will produce different addresses.

As long as the entropy provided by the system used to generate the address is sufficiently random, keys produced by vanity gen are as good as keys produced by any other program that would have used the same entropy.

Naturally, you should be verifying that the binary you are running matches the source code, and is using a good source of randomness, before moving any funds to those addresses.