I think if it increases the benefit, it will be very appropriate.
To ensure you don't sound like adding up tasks to others, the approach that I would take is approaching their manager, explaining to them the benefits of this conference if your non-direct reporting colleagues attend this.
If their manager approves that it should be easier for you to suggest this to them as well. If you cannot approach their manager, just approach it through your manager of the same level, and he/she will forward this invitation to them.
