Electronic – PIC/ICSP – Protect circuit from VPP voltage

From Microchip's In-Circuit Serial Programming Guide:

So the diode provides \$V_{DD}\$ to the MCLR pin when the ICSP connector is not connected or when \$V_{PP}\$ isn't present. This must be a Schottky diode.

Resistor in Vdd line.
Added RM - Steven can edit as/if desired:

Reason not 100% certain but note it is shown as a resistpr or a direct connection.
On page 2-2 of the data sheet it says:

• Interface to the Programmer
  The cable length between the programmer and the circuit is also an important factor for ICSP. If the cable between the programmer and the circuit is too long, signal reflections may occur. These reflections can momentarily cause up to twice the voltage at the end of the cable, that was sent from the programmer. This voltage can cause a latch-up. In this case, a termination resistor has to be used at the end of the signal line.

Yes, that particular PIC can be programmed with the low voltage method. That requires only ordinary digital signals to be connected to MCLR, PGC, PGD, and PGM. The drawback is that low voltage programming must be enabled. Unprogrammed parts come that way from the factory, and it is impossible to disable it over the LVP interface, so you're probably fine unless you are trying to re-purpose a PIC previously programmed with the high voltage method.

As a programmer, it should work fine for the limited set of PICs that allow for LVP and are configured to allow it. My PIC programming introduction gives more background on PIC programming. This only discusses the more common and more general high voltage method, but should give you some good background nonetheless.