Depends on what you're going to do with the website/portal. If you distribute that as a product, the GPL prevents you from distributing the forum unless you GPL the rest. If you use it as a website custom made for a customer, you're fine.
GPL forbids distribution of binaries from the sourcecode without the sourcecode. It's debatable whether it's distribution if you create a website for 1 customer and pass it to the customer.
We made it GPL to avoid having others sell the forum code as a product. We didn't make it GPL to nag onto our customers of course. So unless you're selling the forum as part of a product (to as many customers as possible, so no custom made stuff), you're fine.