"The 89C51Rx2 family is fully compatible with the 87C51."
Does this means that it can be programmed in 87c51 parallel programmer ???

The most often changed about a given derivative is the programming algorithm and that, as far as I know, has NEVER been a reason to declare a chip "not compatible". For instance for "plain" 87C51 Atmel., Philips and Intel are not just "compatible" but IDENTICAL, but still require different programming algorithms.

so your question has 4 answers (in sequence of lileyhood)
1) no (one is fuses, the other is flash)
2) no and will burn the chip
3) yes, but endurance will suffer
4) yes

If you are willing to take a chance in 1) 2) or 3) go ahead, I would not.

Anyhow, since the 87C51 never had a boot vector, how will you go about that.

Erik

a comment:
Like many other organizations, Philips first line answers are rarely "very intelligent", you need to "punch through" that line to get the full and unadulterated answer. I'll try to see if a contact will chime in here.