Are non-GFCI outlets that are downstream of a GFCI outlet ground fault
protected if they are fed from the GFCI outlet's load side?
If those non-GFCI downstream outlets were not fed from the GFCI
outlet's load side but rather just had their hot, neutral and ground
wires spliced to those feeding the GFCI outlet, would the effect be
the same as if there was no GFCI outlet on the circuit at all?
Yes. The GFCI outlet will only protect its own outlets and any outlets that are connected via it's 'Load' connections. Anything spliced before the GFCI will behave as if there is no GFCI.
The most important thing is to make sure you connect the GFCI to power from the panel via the 'Line' connections. If you connect to the Load connections, the GFCI functions just like a cheap $1 non-protected outlet, and provides no extra protection.