When it is clear, maybe - but most of the time the trap that questions fall into is seeking legal advice that we can't give.
Most of the time the only answer without possibly giving them harmful or misleading advice is "Ask Canonical" - http://www.ubuntu.com/legal/terms-and-policies/contact-us - that address specifically for how Ubuntu and it's logo can be used.
Examples (against):
https://askubuntu.com/q/666635/47291
Can I use the Ubuntu logo on t-shirts produced non-comercially? (quoted text has changed, many say things like "It's Fine!" - when it may not really be...)
Am I allowed to display the ubuntu logo?
Is it possible to create Ubuntu Shirts ( Merchandise )
https://askubuntu.com/questions/592514/can-the-ubuntu-logo-be-used-for-my-business?rq=1
Is it legal to use Ubuntu name for my cybercafé? - three link answers saying "ask"
Examples (for):
Can the Ubuntu logo be used for a commercial website? - answer is clear
