Software RAID should work fine. It all depends on how many VMs you will be running and how IO intensive they will be.
The article you pointed to is four years old, and was using ZFS instead of OpenFiler but for a few VMs it should be fine. Keep in mind the statistics they pointed to were using an EMC Clarion array with 40 disks. You are using 4, so your thoughput will be much lower. They also don't quote IOPs in the article, or the exact test scenarios. Dedicated storage processors (such as those on an LSI card) are good at prioritizing and queuing requests, which leads to higher IOPs. IOPs tend to be much more important then throughput.
Throughput will be a concern, though, since I am guessing you will be using GigE and your server as an iSCSI target. GigE is much more limited then a dedicated bus (PCIe) for storage throughput. Again, in small scenario this shouldn't be an issue.
I would go with the software option, unless you are using the VMs for storage intensive applications (or more then 10 active VMs).