Which of the following is grammatical?
- Managers are one group to which these findings are relevant.
- Managers are one group to whom these findings are relevant.
Relative pronouns tend to refer to the most recent noun, and here the most recent noun, is group. Group could be perceived as inanimate, but in this context, at least, it is clearly a group of people, and that makes whom appropriate. That choice is reinforced by the fact that managers is the topic of the discussion.
If you wanted to avoid the choice altogether, you could say ‘Managers are one group that these findings are relevant to’, but there are those who would object to that on stylistic grounds.