Well, if porcupines can manage, I'm sure the Hork-Bajir have it figured out.
(pro-tip: Never attempt to tooth-and-claw kill a porcupine. It may seem like a good idea at the time. But, oh, the horror...)
And yes, platypuses are weird. Internal fertilization, oviparous, and yes, dear Virginia they do lactate. Weird, even by Earth standards.
(side note, can you imagine this convo happening?
Tobias: *awkwardly explains lactation*
Ax:
Epic lulz there.)
If I recall correctly, the bit in TAC about the wishflower at least implies that gestation is fairly long. Which would suggest placental vivipary on Earth, but hey, like I said, there's precious little cannon evidence to go on.