Generally, spoke to spoke works even with hub to spoke topologies. Of course, such traffic must transit the hub. If that's what you're trying to avoid, as mentioned by the other poster, DMVPN (at least the latter variants) can construct tunnels spoke to spoke. There are considerations using this feature.
It might also be possible to construct/configure another (temporary) tunnel for the (direct) spoke to spoke communication. This may be better than using something like DMVPN's feature if there's only one pair of spokes you wish to interconnect. DMVPN would be better if you wanted to allow any spoke to communicate (directly) with any another spoke.
