Generally speaking no but there are some like the Siberian orchestra who do use them
There is no guitar in a standard symphony orchestra. If the orchestra is playing a guitar concerto, the guitarist would sit in front of the orchestra, near the conductor, as would any other soloist.
Don't you mean "why isn't a guitar in an orchestra" Orchestras have traditional arrangements and the guitar is not part of that. They weren't around when the orchestra form was invented and it would be too weird to include a guitar in an orchestra now.
No, unless a particular piece of music calls for a guitar in which case the orchestra can be supplemented.
Electric guitar
guitar
The harp and guitar are both, sometimes used in the orchestra ( the harp more than the guitar ). The instrument known as the "harp-guitar" is a very rare hybrid instrument. Most of its repetoire is in solo pieces and chmber music. It is not a regular member of the symphony orchestra.
no
Guitar Slinger - The Brian Setzer Orchestra album - was created on 1996-04-23.
a guitar.
Al Viola
Bass Guitar viola and violin