RE UI vs severance, it varies by state, Here is what CO says at
https://www.colorado.gov/pacific/cdle/wage-information
"Vacation, Severance, Pension or 401(k)
If you received vacation, severance, pension, 401(k), or some other form of payment from your employer as the result of your separation, this may reduce or delay your benefit payments. You will receive a Notice of Decision if this happens.
For example, if you receive vacation pay because you were separated, your claim will be delayed for weeks equal to the amount of the payment you received. This delay begins the week you become eligible for benefit payments."
Also, a lump-sum payout could have negative tax implications since the payout would be taxed all in the same year. Possibly pushing you into a higher tax bracket. Especially if paid late in the current year. If lump is paid next year, then it is only a problem if he finds a new job early in the year. Effectively getting paid twice for 25 weeks.
You should consult a tax professional as there are other variables to consider.
PS there is a sub-forum for Unemployment issues at
http://www.city-data.com/forum/unemployment/