I'm assuming that you'll be instructing on Heli's. As long as your company don't mind you instructing on the side, many schools would love to have an experienced guy coming in to help. What the other instructors would think is a bit different tho'.
Heli instructing is a bit different to fixed wing, in the way that most instuctors aren't simply hour building until they get enough hours for the airlines. Less likely to think that you are 'nicking' the hours that are rightfully theirs.
Some schools are more receptive to part-timers than others. Often you'll be asked to help out at rush times etc..
There is always a great debate on the merit of part time V. full time instructors but I've always found most experienced part-timers to be as good as anyone else.