Did the Geothermal Power Plant contribute to Pahoa's Lava Fissures?
I think we can confidently enough answer "no".

From this report (p. 23):


  Kilauea eruptions occur either at its summit or within two well-defined swaths (called rift zones) that radiate from the summit.


In the same report, you can see those rift zones on the map page 3, or on the sketch of the plumbing system page 24. Most lava flows are emplaced along these rift zones. For instance, look at this map of the 1955 eruption (public, USGS):



You can see that the flows were emplaced in a zone very similar to the 2018 eruption. Apparently the power plant opened in 1993, and the first exploratory wells were drilled in 1961-62, so after this event.

Actually, the rift zones are in the lava flow hazard zone 1, i.e. the most severe. The zone is defined as follow by Mullineaux et al. (1987):


  Zone 1 consists of the summit areas and active parts of the rift zones of Kilauea and Mauna Loa; in those areas, 25 percent or more of the land surface has been covered by lava within historical time, during the 19th and 20th centuries. These areas contain the sites of most historical eruptions, and a large majority of the lava flows that will affect other zones on Kilauea and Mauna Loa in the near future probably will originate in zone 1. [emphasis added]


So the real question is: why was the plant (and estates...) built in an area well known for lava flow hazards?!

To conclude, by researching the plant I found that it is actually where people accidentality drilled through a magma pocket for the first time (Teplow et al. 2009)! They hit a pocket of dacite; it did not trigger an eruption. This happened later in Iceland: this time, they even used it as an experimental well (there is a whole issue of Geothermics on this). Again, no eruption.