I am having a number of issues with the current onboard NIC on my older vSphere host so I am looking at retiring it however before I do there is a lot of data I need to pull from the host and the stuttering NIC is not upto it; if I am to simply put a new gigabit NIC in the chassis then is it likely to cause any issues with current VM's and is there a way to install drivers if it is not automatically recognised?
Make sure your NIC is listed as supported in VMware HCL.
Then if it is, you make sure you use a supported combination of Driver and Firmware for this adapter.
You should not have too much issue, depending of the type / brand of adapter to find driver and FW.
Once you have that you can always install the new driver using update manager / esxcli software update vibs, or by following the installation instruction of the driver package.