Yes, sometimes you can get by with no decoupling cap across Vcc and Vss when programming with the PK3, but there are many threads on the Microchip forums in which such caps are recommended when using that programmer. Here are just two:
https://www.microchip.com/forums/m897087.aspx and m690219.aspx . In each of those cases, the author is "Ian.M." In my own experience with the 12F683 and PK3, a cap along with reducing the programmer voltage to slightly less than 5.0 V cured the problem (target powered by programmer mode). The power supply on the PK3 is not very robust. If you put a scope on it and watch Vcc, you can see it sag significantly when programming.