Its all up to your AHJ,
Since utilities don't require XLPE messenger cable to be UL listed manufacturers don't bother using a NEC 310 type wire when making the cable.
Utilities also size the ampacity of the cable based on the manufacturers instructions.
My take is, and others on here will disagree, the NEC allows us to do the same, 396.10 says there is a table of permitted messenger cable types and go by the NEC code article that matches the cable type in the 2011 NEC table:
396.10 Uses Permitted
(A) Cable Types. The cable types in Table 396.10(A) shall
be permitted to be installed in messenger-supported wiring
under the conditions described in the article or section referenced
for each.
One of the entries in the table is Other factory-assembled power cables that are identified for the use and no code article. Note the use of the word identified and the definition of identified:
Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular
Code requirement.
The fact that the utilities all over use the cable according to the manufacturers instructions that makes it Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth.
So I'd say if your running non-listed utility triplex as a outside feeder similar to how a utility does, terminated with 90c connectors in free air as a utility does then its fine to use the manufacturers ampacity table.
