Is USE-2 or RHW-2 individual wire fit for direct burial or open-joist use?
USE-2/RHH-2/RHW-2 can be direct buried, but otherwise requires a raceway

The rules for USE-2 wire and cable can be found in NEC 338.12(B):


  (B) Underground Service-Entrance Cable. Underground
  service-entrance cable (USE) shall not be used under the
  following conditions or in the following locations:
  
  (1) For interior wiring
  
  (2) For aboveground installations except where USE cable
  emerges from the ground and is terminated in an enclosure at an outdoor location and the cable is protected in
  accordance with 300.5(D)
  
  (3) As aerial cable unless it is a multiconductor cable identified for use aboveground and installed as messenger-
  supported wiring in accordance with 225.10 and Part II of
  Article 396


This, practically, limits single-rated USE-2 wires and cables to direct burial applications, or use as a multiplex cable-in-conduit outdoors.  (You can't use it indoors or for general aboveground work, even when in a raceway!)

However, when the wire has a RHH-2/RHW-2 rating as well, that changes the picture.  Now, the wire is rated for use in raceway, as the table 310.104(A) entry for this type of conductor specifies a flame-retardant insulating material.  However, it still cannot be used strapped to joists bared, as this violates NEC 300.3(A):


  (A) Single Conductors. Single conductors specified in Table
  310.104(A) shall only be installed where part of a recognized
  wiring method of Chapter 3.
  
  Exception: Individual conductors shall be permitted where installed as
  separate overhead conductors in accordance with 225.6.


and NEC 398.10 only permits the use of open wiring on insulators in industrial and agricultural occupancies:


  398.10 Uses Permitted. Open wiring on insulators shall be
  permitted only for industrial or agricultural establishments on
  systems of 1000 volts, nominal, or less, as follows:
  
  (1) Indoors or outdoors
  
  (2) In wet or dry locations
  
  (3) Where subject to corrosive vapors
  
  (4) For services


while NEC 394.10 only permits limited use of knob-and-tube to extend wiring in existing buildings, and 394.12 point 5 also prohibits the use of K&amp;T within insulation:


  (5) Hollow spaces of walls, ceilings, and attics where such
  spaces are insulated by loose, rolled, or foamed-in-place
  insulating material that envelops the conductors


Even though you can use it in conduit, you probably shouldn't

Even though tri-rated USE-2/RHH-2/RHW-2 can be legally used in conduit jobs, it's probably a bad idea to use it.  Why? It has a thicker insulation than THHN or XHHW-2, which uses up more precious conduit fill area than necessary and makes the wire stiffer and harder to pull as well.  It's also slightly more expensive than XHHW-2, making it a rather pointless choice to make.