Yes, werewolves and vampires can fall in love. While it is possible, it is not very likely to happen. Because there are no rules to love, and because both vampires and werewolves take human form, there are many reasons why love between the two could be possible. The problem is that there are certain things that prevent it from happening in the first place.
The first obstacle is that many – if not most – vampires do not like werewolves. It would require getting over this innate dislike in order for them to even be friendly with each other and get to know one another. Once this obstacle is overcome, then you have the vampire’s innate desire for blood.
While werewolf blood is not the primary choice for most vampires, many hungry vampires will attempt to feed on anything. Yet another obstacle is the preconceptions that each species has about the other – both tend to believe the other species as untrustworthy, arrogant, and a competitor – this taints the initial encounter between any two individuals with feelings of hesitation and wariness from the very beginning.
Having said all this however, it is possible (though again, not very likely) for these obstacles to be overcome and these two species to not only coexist, but also fall in love.
Vampire love stories are at the core of vampire tales, anything is possible.