I have often seen live televised sports matches using upstream English commentaries (by upstream, it means using original international commentators rather than provided by downstream [local station that I watch the match]). So I closely hear what accent the upstream is speaking. According to my experience, most of upstream commentaries are speaking British accents (or some sort of). At first glance, I thought that they are speaking RP (received pronunciation), because they don't pronounce the final /r/ (non rhotic) as well as saying the clear /a/ instead of /æ/ (the characteristic by convention [which isn't written in articles about British accents]).
This led into conclusion that in order to be commentators, I had to speak British accent (that is, imitating the way they are speaking). Then I tested the hypothesis by asking in Physics Forums. The hypothesis got rejected. One of the commenters there said (with edits):
No. Wrong way to make the decision. Model your pronunciation the way you are taught or are able to acquire. Your ESL teachers probably have their own accents. You may follow those accents or attempt to make a neutral accent ( I am not sure if this is meaningful). Sports commentators in other countries (upstream in this case) have what accent is appropriate for each individual announcer/commentator. This is not something which a person changes to nor from. On the other hand, a few individuals do adjust their accent, but again, I am unsure how common this is.
Later in the thread, another commenter said why RP isn't the case nowadays (note: below is UK-specific, although that I also see matches in other countries/regions [most are European]):
Unless you have been listening to sports commentary from the 1950s, RP is a thing of the past. British television presenters speak with a range of regional accents. Most use what might be called "careful" English - words and phrases that are in general use. The last of the great RP commentators was Henry Bloefeld (and, yes, Ian Fleming did use that name as the Bond villain). He was a radio cricket commentator for decades and made the most of his Eton accent. He was wonderful to listen to. But in my lifetime the great voices of sport have had a range of accents with the RP speakers gradually dying off: Henry Longhurst for the golf, Dan Maskell for the tennis and Bloefeld for the cricket. These days your best bet is a Scottish or Welsh accent, I would say.
From these above, the verdict is: It's OK for aspiring commentators (and myself) to speak whatever accent they are comfortable with (in my case, General American accent due to computer demand). However, with exposure, it's possible to change the accent over time (in this case, I may develop British accent due to sports commentaries).
Thanks.