There is no Import tool available to migrate from Boonex's Dolphin . Better to follow Emil's suggestion and post a Job at Oxwall's Market and other Free-Lancer communities
May I know why do you want to migrate from Dolphin? Looking for migration from Dolphin is too complicated. I myself don't recommend to migrate. It's not that easy to make use of Oxwall to get all the Dolphin's features(for which you used modules)work on Oxwall.
3 Steps to avoid Fuss with Migration
I can suggest you to build a new Oxwall Network and....
1) implement Single-Sign-On by utilizingFacebook connect which is available for free of cost
2)Then make use of the Great and light weight Oxwall for some features(like Groups, Chat etc.) to your Network and keep the Current Dolphin network a side for forums and video sharing modules .
In that way you need not trouble your currently registered members and provide them a great feel with new features
The third step is to ...Customize the style of your new Oxwall website. So that it's theme would match to your Dolphin Based site. In that way,Your members will not get confused with the new look :)
Good Luck !