Yes it will be. The ones that will fly will be in a stack themselves, we have an RTC board which goes on first and then the Astro Pi goes on top. This is because the Pi isn't allowed on the ISS LAN (not for this mission anyway) and would have no means of getting the time from NTP etc. All the kids ...

Since CubeSATs use PC-104 boards and they survive for relatively long periods in the vacuum of space, PIs should be able to survive in orbit if the overall system can handle the thermal conditions.