I would imagine in such a case exploits would be very rare. It would need to be a very specific exploit and yes there is little scope for what can be exploited

I would imagine in such a case exploits would be very rare. It would need to be a very specific exploit and yes there is little scope for what can be exploited as it FPGA is designed for very specific task unlike a general purpose CPU in server. You would need to have deep knowledge of the HDL to even begin to think up an exploit.