The function $\log_{1/5}$ is decreasing, so your inequality is equivalent to $$ 0<\log_3\frac{x-3}{x+3}\le 1 $$ which in turn is equivalent to $$ 1<\frac{x-3}{x+3}\le 3 $$ The left hand side inequality is $$ \frac{x-3}{x+3}-1>0 $$ or $$ \frac{-6}{x+3}>0 $$ that gives $x<-3$.
The right hand side inequality is $$ \frac{x-3}{x+3}-3\le0 $$ or $$ -2\frac{x+6}{x+3}\le0 $$ which gives $x\le-6$ or $x\ge-3$.
Putting together the two inequalities gives, as solutions, $x\le-6$.
Note that your interval $x>-3$ is wrong. For instance, if $x=0$ you get $$ \frac{x-3}{x+3}=-1 $$ and the logarithm is not defined. You forgot the condition that $\log_{1/5}t$ is defined only for $t>0$.