Given that there are some languages that treat /r/ and /l/ as a vowel, such as Czech and Hindi, I am wondering how come the same isn't true in some varieties of English.
As a native English speaker of the American West, I have noticed that we pronounce many of our /ə/ + /ɹ/ and/or /ɫ/ using just those liquid sounds.
The best example is how every Arabic speaker I have met has trouble with the pronunciation of the word "world", and usually realizes it as something like [ˈwɔr-lɛd]. I only noticed that when I try to explain to them how I pronounce it, I have to omit all 'vowels'; [ˈwɹ-ɫd].
In the pronunciation around Los Angeles, it seems many of us follow this pattern with a whole category of words including:
pattern - [ˈpʰæ-ɾɹn] or [ˈpʰæɾ-ɹn]
stirred - [stɹd]
measure - [ˈmɛ-ʒɹ]
It doesn't seem to be accepted practice to consider these liquids as vowels at least by dictionaries or Wikipedia, but when I try to pronounce these words the way the authorities presume, it sounds like I am speaking with a different accent.
As a caveat, I will state that I've heard virtually only exceptions to this from speakers anywhere east of Denver, Cheyenne or El Paso.