As a coach I've learned that an ideal candidate for pole vault at a high school level is a kid who can run the 100 in 12.0 or faster, can long jump 19' or further, can do a back flip on command,is fearless, patient, follows instructions well, and has strong upper body strength (not to be confused with having a large upper body).
Some distance runners have the ability to run and jump to those marks. Most don't. If they are running a low 9 3k or better it's in their best interest to continue with that than to be undermining their true talent.
You have to ask them whether they want to be be a half assed distance runner / pole vaulter or a great distance runner.
So it really depends on the athlete. If I have a guy who is running 10 minutes for a 3k and he has been at it for a while,is coordinated enough then I might let him try it.
One important thing to remember about the pole vault. If you have an athlete that cares a lot about self preservation then they will not be good at the pole vault and to a certain degree they are in danger of not getting that pole verticle and reaching the mat. They have to be fearless. If they slow up on the approach it can be dangerous for them. There are kids I will not even let try simply because I don't want to kill them.
Also, if you're a coach you should get certified as a pole vault coach. If you're an athlete make sure your coach is certified. This is a dangerous event for those without knowledge.