What does indirect evidence have to do with it?
The reason ID is not considered science is because of the difficulties inherent in knowing the design status of an object when nothing is known about the designer. It does no good to have as many false positives as correct results. Get the people at DI to fix the problems with ID then talk about getting it into science.
Indirect evidence has a great deal to do with science, and vise versa. The evidence for intelligent design is largely indirect. The only inherent difficulties in ascertaining whether an object is designed or not occur when there is no physical matter to observe or quantify, IOW total chaos. Put another way, if all the universe were a black hole, intelligent design would perhaps be sorely lacking in physical evidence.