1)
Do the oases drip?
1.
Rashi: Shamayim drips [rain] onto the oases. Radak - just like it drips in Yishuv, also in the Midbar, so the Chayos will find food and drink.
2)
What is the meaning of "v'Gil Geva'os Tachgornah"?
1.
Radak: This is a metaphor. When the hills are full of produce, it is as if they are girded with Gil (joy) in place of girding sackcloth when rain was withheld.
2.
Malbim: This refers to the settled areas, corresponding to "Atarta Shenas Tovasecha" (verse 12). "Yir'afu Ne'os Midbar" corresponds to "Yir'afun Dashen" (ibid.)