I couldn't find any info on whether this plant is safe for rabbits. If the fruit is safe for people to eat, then it may also be safe for rabbits, but I couldn't venture a guess about the rest of the plant.
Longan seems similar to lychee (which rabbits can eat), so it's probably safe. Just remove the seed, and feed in small quantities as it is high in sugar. I may be wrong, but it seems okay.
It is still worth checking out the facebook groups mentioned above.