It really all depends on what you're talking about. There are several kinds of love. My preferred models are the
seven love styles and
triangle of love. If you're talking about love that is primarily driven by
passion(see,
Eros,
Ludos, and "love at first sight"), then, no you don't need to know them well. For love driven by
intimacy (See
Strogma), then, definitionally, you do. While it is possible to have a love primarily driven by
commitment (see
Pragma). Relationships driven by
mania tend to be very toxic to those involved, as that relationship maintenance involves a ton of cognitive dissonance. Western societal expectations dictates that love involve at least passion or intimacy, but
mania tends to lack these. So the partners struggle with believing they must feel these emotions, but don't actually.
The important part to remember here is that it is easy for one type of love to shift into another, and that over the course of possible relationships the type of love and relationship will change. The prototypical relationship in America (at least, I think this generalizes to most of Europe, and I'm not sure about beyond that) starts with
Eros/love at first sight, then shifts into
Romantic love. Then, in healthy relationships that expect to "last forever," This shifts
Compassionate love (where the sex dies, but the love lives on) and
Consummate love (where the sex doesn't die), and will continue to shift between these two. In "doomed" relationships, the
Romantic love can become
Manic,
Fatuous or
Empty love.
So, basically, you don't need to intimately know someone before love and/or commitment can begin, but you do need to get to know them for the relationship to continue and be healthy.
[massive hyperlinking for defining massive jargon usage.]