Expected behavior: Mutagen Producer can use U235, U238, and Uranium Blocks from IC2 (when it is installed)
Tested behavior: U235, U238, and Uranium Blocks cannot be inserted into the Mutagen Producer

After some investigation, I found that the problem seems to be on line 201 of the file:
/resources/assets/gendustry/config/recipes.cfg
should be:
if HaveMod ic2 {
instead of this:
if HaveMod IC2 {

Mod Version: 1.6.5.8
MC Version: 1.12.2
Tested with:

• Forge 14.23.1.2608
• BdLib 1.14.3.12
• Forestry 5.7.0.238
• Gendustry 1.6.5.8
• Industrial Craft 2.8.51-ex112