Can be, depending on the configuration you would like to consider. In a DEXTER personal cluster there are four computers (we also call them nodes). One always has an ATX-size motherboard, we call it the Master node. This is the one which has its connectors visible on the back panel of the DEXTER cluster case.
The other nodes (we call them slaves) may have an mATX-size motherboard but the CPU and memory type is always the same as for the master node. If they are all ATX because the CPU can only be fitted in an ATX-size motherboard, then there is no difference among the types of motherboard and of course CPU’s are the same as well.
Other components may be different like the number of hard drives attached to the slave computers.