I can give an insight from a personal experience. I am on a skilled worker visa, and I managed to do a vacation scheme at
Macfarlanes. They allowed me to do the vacation scheme, however, I had a specific schedule that does not exceed 20 hours/week (My current job is in the same field). I was lucky to have these conditions because their policy of assessing candidates was based only on the assessment day at the end of the vacation scheme, and not on your performance during the two weeks, otherwise I will have less time to show my skills.
I would suggest to ask GR teams in advance to see if they allow you to do the vacation scheme.
Hope this helps.