The software does work on ARM boards like the Raspberry Pi. There's a linux-arm download for it: https://github.com/decred/dcrd/releases However, the voting mechanism is designed for low-latency and the slow processing of the original RPi may cause you to miss votes. I'm not 100% sure if it is adequate or not so it's more of a "should work but not recommended" situation. You could always give it a try on testnet first.
Ive been using R Pi 2 for my stake wallet and never missed a vote. I also have battery back up for Pi and Modem in case of power outage. Connected to modem via RJ45 and on a semi decent DSL connection (25Mb) Not sure how an original Pi will handle it though?
I also have a Raspberry Pi 2 setup for staking running Ubuntu LXDE. The Raspberry Pi is painfully slow at processing the blockchain (only does a few blocks per second when downloading from the first block), but once it catches up I don't believe there is any latency. I wouldn't rely on it as a main voting mechanism, but it is definitely a good backup to have just in case your main voting machine goes down. I don't have the original Raspberry Pi, but: The new Raspberry Pi 2 is slow. The original Raspberry Pi will be even slower - so I don't think it will handle too well.
I've been using an Odroid xu4 for stake mining, and it works great so far. I know that the raspberry pi is not as powerful, but I'd imagine that it would work fine.