There are two issues at work here.  The first is the likelihood of spills from that source and the second is the regulations. The question caused me to go back and perform a memory check with regard to the regulations, and at one time, not all facilities were required to have an SPCC Plan if they did not have any likelihood that they could have a spill. (See Section 112.3 for requirements ).  The test is good engineering practice. That doesn't necessarily require a double wall piping system because those systems are not necessarily trouble free, and are often a pain in the neck to install. Depending upon the assessment of potential damage, I might recommend a sheet metal gutter system, suitably caulked to prevent leaks, which is installed under the portions of the exposed piping of concern. The gutters can be drained to a small containment basin locally installed and monitored, and the piping, if it is pressure checked periodically (say once per year or as required) should last a long time. If there is concern, a catch basin may be easier to install than trying to drain the piping all the way back to an containment area. If there is concern about it, install an oil monitoring device (conductivity probe) or even a water level meter would work so that you have time to get to the problem and check it when the level alarm goes off.

As far as materials of construction, there are no really bad materials.  PVC will work just fine as will sheet metal. Again, if it were me, and the piping were fairly standard, I'd use a nominal 1/2 pipe installation set just below the pipe as an oil trap. Support it with straps and hangars as you would, but drain it to somewhere you can catch the oil. The point is to give yourself a fighting chance rather than to make it idiot proof. (When you make something fool proof, Nature invents an improved fool).  The point is that visual inspection is still your best bet for leak control, and if you provide a catchment system, almost any catchment system beneath the pipe, that should be adequate.  It depends upon what the certifying engineer considers "Good Engineering Practice" as defined by Section 112.7 of the regulations.

To summarize:  1) use a half pipe of almost anything and install it beneath the existing pipe in the area of concern.  If the distance is too great, drain it to a catch basin which you visually inspect each time it rains. The catchment piping can be anything which does not leak, but I'd probably use PVC of a size large enough to cover the oil carrying pipe flanges with some room to spare.  So if you have a 4" pipe, your final drainage pipe may be 8" - 10" so that it can go around the pipe flanges, or 6-8 inches if the pipe is continuously welded.