That's correct. Generally TE tunnel is either dynamic or explicitly defined. In dynamic path, you just need to configure tunnel destination's ip address, ignoring in between hops in the paths whereas in explicitly defined path you need to define/mention all the hopes involved in the paths to the destination.
However, if you want to have automatic path calculations and automatic rerouting of IP traffic onto MPLS TE paths, you have to use dynamic tunnel with OSPF or IS-IS. Here link state protocol (IS-IS or OSPF) is used with enhanced link state advertisements to track network capacity and to ensure that the tunnel does not create a routing loop. The actual signaling for dynamic tunnel establishment is based on RSVP, which acts to reserve bandwidth on a link.
Also, in some cases, MPLS-TE tunnel can be configured to use multiple paths (explicit as well as dynamic) from the source to the destination so that it can choose the path it needs in the order of preference.
So now to answer your questions:
You don't require IGP if you are using explicit path. Although I haven't tried configuring explicit path alone in lab/real world, but considering RSVP's function, I guess that you don't require RSVP in the case where you are using explicit path only.
Also you are right when you say that IGP(OSPF or ISIS) is required in order to make dynamic path work as these two protocol(OSPF and IS-IS) have been provided with extensions to enable their use in an MPLS TE environment to propagate information pertaining to resource availability and in dynamic LSP path selection.
To give you real world scenario, in our SP network design, we are using dynamic tunnel with OSPF as IGP and no explicit path at all.
HTH.
