Well, it isn't the highest affiliate commission from a hosting company I've seen, but if you are 100% committed, confident and know this company well, give it a shot.
At 5% level, the question becomes whether it is worth spending your time marketing the company to receive your commission versus perhaps getting into actual reselling. First let's you focus on marketing only, while the second obligates you to get involved in operating a hosting company of your own. Nothing wrong with either options and there are a lot of people out there who prefer to just concentrate on sales/marketing to avoid the headache of running your own company.
Is the 5% recurring or a one time commission?
You have to consider all the factors: how much will you be putting in vs how much you'd be getting back in return and how much would you get for the same time / placements on your website if you used another companies affiliate program.
They seem to focus on dedicated servers which could be great for you. They don't offer $5 - $10 shared packages and jump right into $100+ dedicated servers so you won't be seeing too little pennies with that 5% commission.
The negative side of that is they might be alienating some of your visitors who do not require a dedicated server.
A key question would be is the 5% recurring or a one time offer? If it is one time, you're better off finding another affiliate program. For a $200 server you'd get $10, at other affiliate programs you could make $85+ per sale and that includes a much wider product portfolio (shared, VPS, reseller and so on).
also to take into account is
1) what is the min. commission before you can withdraw
2) can the commission be withdrawn to paypal etc. or is it just added as a credit to use on future purchases from them
It is recurring.