Using a transistor as a diode?
From your question, I can't really figure out how your circuit works. But I can answer the question if you can use transistors as diodes with "yes".

One example where this is often done in discrete (non-integrated) circuits is when you want to have a diode with a very low leakage current: A diode-connected transistor (C and B terminals shorted together in order to use its B-E-diode) has much lower leakage than most regular diodes.



(Source: Linear Technology App'Note 43 by Jim Williams)

Just make sure you pay attention to the absolute maximum ratings of your transistors for the "blocking direction": The maximum allowed negative B-E-voltage is quite low compared to diodes.