You can program in teams with ten or in companies with hundred Lisp developers. Usually the team size does not need to be that large.

Lucent for example developed a Lisp based network switch (similar to what Ericsson did later with Erlang) and they had around 100 developers. It was competing with a much larger team developing a similar product in C++.

ITA had around 100 developers for their flight search in Lisp.

Symbolics had at its height around 1000 employees and my guess would be that 40% were Lisp programmers.

Personally I'd say there would be little problem working in a team with ten Lisp developers - you just have to find or educate them.