That kinda depends on the level of taxation applied to the corporates and those who chose to supplement their UBI by doing some additional work for extra income, which would therefore be taxable. If you have enough revenue from taxation to cover everything else with a surplus, then UBI can be raised above "subsistence level" (which the minimum it would need to be if it's supplanting most current forms of welfare) to something a bit more comfortable. OP is probably right on the "not everyone" front though; if it happens, UBI is going to replace some current unemployment benefits outright, and there are plenty of examples of people who don't manage that income wisely, so we shouldn't expect that to change just because it is - from their perspective - just given a different name?
However, on the face of it, and given UBI experiments have shown recipients still tend to seek out and undertake some work, that would still tend to indicate most of the taxes necesary to fund it are going to have to come from corporates and investment income. In otherwords, reducing the incomes (in the form of bonuses and dividends) of exactly the kind of people who, as TFS demonstrates, are the least likely to want to pay those taxes just so others don't have to work, even thought they've probably never actually done a hard day's work in their life either. So, while I think UBI could absolutely work in principle, I suspect it's going to be a real mixed bag as to how well, and how comfortable the lives on it without supplementary income is likely to be. Where capitalism is king, like the US, UBI would never, ever, get above a level that doesn't even qualify as "subsistence", but I think it would definitely have a realistic chance in places like Scandinavia where they've long since accepted high taxes are a necessity for a higher overall standard of life, and - strange as it may seem - the Middle East where personal taxes tend to be near zero anyway.