I'd say in general, yes. Roach poop would be decent plant fertilizer. They are one of the last detrivores on the food chain. In nature, most tropical cockroaches feed on decaying leaves, fungi, fruits & other vegetation.
As far as what you feed your roaches, that would reflect on the nutrient values. Plants typically need varying amounts of the following: nitrogen, phosphorus, potassium>>these are the macro-nutrients. Next is the micro-nutrients: iron, zinc, boron, copper, magnesium, manganese, chlorine & a few others. There are also trace elements included in the mix, too.
One of the best fertilizers is derived from seabird guano & seaweed as well as fish derived fertilizers. The ocean water contains all nutrients & is assimilated into organisms & algae in varying amounts.