Is Weezer emo?

Answer

Not really. They're more Pop-Punk than anything. Although the album "Pinkerton" is considered Emo, it is the black sheep of their work. It's different from the rest of their work, it's much darker. Weezer is sometimes labeled "emo" because of lead singer Rivers Cuomo's glasses.
As the above satement says weezer is more pop-punk not emo....pop punk is a form of emo music so to answer the question, yes weezer is emo....
source::Wikipedia
Emo (pronounced /ˈiːmoʊ/) is a style of rock music typically characterized by melodic musicianship and expressive, often confessional lyrics. It originated in the mid-1980s hardcore punk movement of Washington, D.C., where it was known as "emotional hardcore" or "emocore" and pioneered by bands such as Rites of Spring and Embrace. As the style was echoed by contemporary American punk bands, its sound and meaning shifted and changed, blending with pop punk and indie rock and encapsulated in the early 1990s by groups such as Jawbreaker and Sunny Day Real Estate. By the mid 1990s numerous emo acts emerged from the Midwestern and Central United States, and several independent record labels began to specialize in the style.
Emo broke into mainstream culture in the early 2000s with the platinum-selling success of Jimmy Eat World and Dashboard Confessional and the emergence of the more aggressive subgenre "screamo". In recent years the term "emo" has been applied by critics and journalists to a variety of artists, including multiplatinum acts such as Fall Out Boy and My Chemical Romance and disparate groups such as Coheed and Cambria and Panic at the Disco.
In addition to music, "emo" is often used more generally to signify a particular relationship between fans and artists, and to describe related aspects of fashion, culture, and behavior.

Emo is Emotional Punk or Hardcore, Weezer is not Pop-Punk and Pop-Punk is not Emo, MCR(Pop-Punk), Coheed and Cambria(Progressive Metal), Panic! At The Disco(Classic/Pop-Rock), Jawbreaker(Punk), and Jimmy Eat World(Power Pop) are not Emo in my opinion... Weezer is either Alternative or Emo.