From a realistic rather than science fiction perspective, the wormhole question is moot. Since black holes are relatively rare, the probability that the singularities of two spatially distant black holes would come into contact is virtually zero, as is the probability that any possible wormhole would lie in a location useful for alien space travel. General relativity dictates, further, that wormholes would be extremely unstable. The longevity of any possible wormhole (briefer than a tiny fraction of a second) is far too brief to allow any physical being (or even any fundamental particle) to travel through.
The most devastating evidence against wormhole travel comes from the laws of physics. In short, any physical object would be destroyed beyond recognition by the intense gravitational forces in the vicinity of a wormhole. An unlucky alien approaching one would be stretched into a long line of particles several miles long. As this alien gets sucked down toward one of the singularities, even the particles would disintegrate. The alien would end up as an extremely compressed ball of chaotic energy.
While wormholes are mathematically possible, they offer no hope or help for alien travel. Even the tiniest physical entity could not survive passage through a wormhole. Coming anywhere close to a wormhole would mean destruction and death.