There are factors pointing both ways here. If getting a job means giving up benefits for the unemployed, or means-tested welfare that you'll become ineligible for, that's a disincentive to get a job. But utility isn't linear in money, and so a job paying N dollars will always be more attractive to someone making zero dollars than the same job is to someone on UBI worth K dollars -- and increasingly so the higher K is. That's also a disincentive.

Which of these disincentives is bigger depends on the sizes of N and K and the specifics of the welfare system. I think I'd usually expect the incentive landscape on the margins to be friendlier under UBI, but it's by no means a certainty.