Two issues really exist:
- Backwards Compatibility
- Analytics Redux
Backwards Compatibility
There is a series of upgrade scripts, procedures, and steps in order to upgrade ECM 2.2 to EXM 3.0. I will edit with link to the Upgrade Doc.
However, as of EXM 3.1, backwards compatibility to utilize ECM links, clicks, opens, and bounces was removed. Along with it, reliance on any of the old AutomationStates table.
The real issue is that the links created out of ECM contain ec_as and ec_camp. These correspond to Automation State and Campaign Id.
In EXM, those were removed and now ec_message_id and ec_contact_id.
Well, if you have access to the old Analytics database from 7.x, you can derive a Membership Profile username. But, EXM utilizes xDB contacts. The upgrade scripts creates user accounts in xDB, but the identifier is domain\username and OOTB EXM wants to use email address as primary identifier. So, without close consideration paid attention to, it's possible to have two Experience Profile accounts for the same person, but different identifiers which causes a host of issues.
So, with EXM 3.3, there's no way to get an xDB Contact from the ec_as query param without major reverse engineering.
Analytics Redux
In EXM 3.3, the entire analytics collection was refactored making any analytics collection from EXM 3.2 invalid. Sitecore did provide some scripts but after repeated tests, found it still didn't upgrade/migrate everything.
SUMMARY
We were contracted by a client doing just that to rebuild the backwards compatibility from ECM to EXM 3.3 It was not an easy lift, and resulted in a number of Support tickets. EXM 3.4 will be coming out sometime in the near future which will support Sitecore 8.2, and I've been told that it's a pretty light weight upgrade
Therefore, if coming from ECM 2.2, and going to EXM 3.3, I advocate working with a Sitecore partner to really hone in on what matters most and figuring out a path.
That's about as much advice as I can give.