It's absolutely true, but it's a pretty subtle thing. On violin, one generally plays notes against open strings to check intonation. Depending on which strings you check against, you will play an audibly different pitch. A string quartet will tend to play in something close to a non-tempered system, depending on the style and the players' ears. Thirds will ring out as nice pure intervals rather than the weird beating intervals you hear from a piano.
But on an instrument as low-pitched and lacking in high harmonics as bass, I don't feel it's very important, especially when playing pizzicato. The margin of allowable intonation error is much bigger on double bass that violin or trumpet.