Hello Harry
When you post a question, try to find a thread that is close to the topic that you are asking about. This is the perfect thread for this question. However, if you find that there is no thread that matches your question, you can always post a new topic, and we may re-categorize it into the appropriate thread.
As for your question, keep in mind that the IP helper address command installed on the local router will just take any DHCP request that it hears on the network and forward it to the DHCP server that exists on a different subnet. This does not prevent another rogue DHCP server on the local subnet from answering the DHCP request since this request is a broadcast and can be heard on the whole subnet. This means that you will still require DHCP snooping in order to protect yourself from rogue DHCP servers.
I hope this has been helpful!
Laz