The host access is configured in two different places. It's a property of an igroup accessing a LUN, and is a property of the LUN itself. The igroup setting defines how Data ONTAP will present it to the host, things like which SCSI error condition will be returned to the host when a temporary problem prevents access to a LUN, or how it will respond to certain SCSI requests. The LUN type setting defines how Data ONTAP will actually lay out the LUN on disk with things like offsets to ensure data is placed on 4k WAFL boundries, has prefix/suffix to hold extra metadata about how to present the LUN to the host, etc.
If upgrading Data ONTAP any settings will be preserved. If upgrading ESX I can imagine that a mismatch in one of these type settings might result in access problems.
I also did some more research and my earlier statement that alignment was OK as-is is wrong; there is a 1 cylinder offset in the solaris LUN meaning if you format it with VMFS it will not align on 4k WAFL boundries resulting in poorer performance. So it would indeed be wise to migrate the data from the current solaris type LUNs to newly created vmware type LUNs.