Question : The operation you selected will convert the selected basic disk(s) to dynamic disk(s) on Windows Server 2008 - negative consequences?

Scenario:
Server running Windows Server 2008 Enterprise SP2.
Server has 2 basic disks "Disk 0" (RAID-1) and "Disk 1" (RAID-5).
On "Disk 0" I have used all available space for "System (C:)" volume, which is from where the server boot.
On "Disk 1" I currently have 3 simple volumes (primary partitions) D: (2000GB), E: (50GB) and F: (100GB), on all of which I have simple file structures (shared to users).
These volumes where created in that order (D:, then E: and finally F:).
On "Disk 1" there is currently +600GB unallocated space.
I now wish extend the size of E: by 50GB (hence reaching 100GB).

I thus (in Disk Management) select the volume, right-click and select "Extend Volume".
This brings up the "Extend Volume Wizard", I click Next> enters the amount of space in MB (e.g. 51200), click Finish.
I then get a "Disk Management" warning stating:
*snip begin*
The operation you selected will convert the selected basic disk(s) to dynamic disk(s).
If you convert the disk(s) to dynamic, you will not be able to start installed operating systems
from any volume on the disk(s) (except the current boot volume). Are you sure you want to continue?
*snip end*

A. Can I be absolutely certain this does not impair the service/functionality of the server, i.e. that it continues to function, booting it's OS from C: as well as maintaining is file structrues?

B. Are there any (eventually other) negative consequences of converting the basic disk to dynamic (such as reduced performance, reduced ability to manage, further extend/shrink, add further volumes, etc.)?

Answer : The operation you selected will convert the selected basic disk(s) to dynamic disk(s) on Windows Server 2008 - negative consequences?

That means Disk 1 is a GPT structured disk.     Unfortunately, Boot-It won't work on a GPT disk, so it's not going to be helpful here.

Your best alternative is to copy all of F: to another drive (external??);  then delete F:    You can then use disk management to extend E: -- and can then re-create F: and copy all the data back.     The only way to avoid that (or something similar) is to convert your disk to dynamic ... which I don't recommend.