I am not finding any single reason to achieve it that way. The main purpose it to display in a report and I think Crystal Report inbuilt facility is enough for accomplishing that, See HERE
Why on a earth you want to format it at VB.net and further providing to report and display by report again.
If you want to go with kind of the thing anyway then you should convert datetime in a format you want using
Method and provide as a
to Crystal report. But Still I am not considering it as a good practice.
You should clarify your question little bit more in details so that intention can be cleared.