Is Camel an ESB?
Typically vendors claim practically everything is an ESB these days, so the answer is probably yes 
However our view is that an ESB is more of a container of integration components, so we view Apache ServiceMix to be a true ESB based around OSGi (and optionally JBI) to provide a standards based integration platform of components.
We view Camel as being a rule based routing & mediation engine which can be used inside a full blown ESB, a message broker or a web services smart client. Though if you want to, you could consider that Camel is a small, lightweight embeddable ESB since it can provide many of the common ESB services like smart routing, transformation, mediation, monitoring, orchestration etc.