With its very varied performance festival, featuring 33 artists over four days, the American Dance Guild salutes key players in the modern dance field. This year's honorees are Joan Myers Brown, founder of the Philadelphia Dance Company (Philadanco); Douglas Dunn, who's been making witty, incisive dances for more than four decades; and Bill Evans, a choreographer and educator whose company turns 40 this year. The companies of all three perform at a gala on Thursday alongside artists like Jody Oberfelder and Sarah Skaggs.