Given your clarification on the Server models the only choice you have for ESXi is to download the generic ESXi Installable version, boot from that ISO and follow the instructions. A base ESXi install is very simple - all you need to know is you host name, main management network ip-adress and network info. Optionally you can plug in an ntp server address and a license key if you like at this stage, or do that later.
It's not possible to add custom management agents to ESXi - you have to get a version with the management tools built in. The ESXi "Console" is just a busybox enabled set of tools running on the hypervisor, it's not an environment that you can or should significantly modify.
That is if you want to use those agents - that will only matter to you if you have a systems management console that you want to use for full hardware management. Even without that you will get a significant amount of hardware level diagnostic data via ESXi (and visible in the VI Client) telling you things about the health of the hardware (various temps, fan speeds, failure stats from the Systems Management and Power Management buses for example). You would get more data and more active control via the Open Manage agent but how useful that would be depends on your needs. If the machines have a DRAC then you will have most of that data and active out of band management capability available directly that way.
As far as RAID is concerned, yes you should configure RAID in advance via the RAID Firmware utility during boot. ESXi doesn't absolutely need local storage but it's a good idea to have some storage visible to it as it likes to configure some scratch partitions (around 5GB in total IIRC). Having these available makes future upgrades and debugging much easier. You wont lose much storage and the install will configure all of the remaining blank space on the boot volume as a VMFS datastore for your VM's.
Which version of ESXi are you trying to install.. I think the drivers for those are now included in 5.1 (I might be wrong though).
Alternatively, you can try to use the Dell customized build of ESXi ISO to install VMWare and see if those include the required drivers you need.
Best Answer
If you're having a problem with a Dell server, use the Dell ESXi image, as it had the agents and monitoring hooks built-in.
It seems like you're trying to ask how to add drivers to ESXi on non-Dell/non-HP hardware. If that's the case...
Use supported hardware.
ESXi is bootstrapped by a small Busybox installation. There are only so many device drivers that can be shipped and supported effectively. Many systems that don't seem ESXi-compatible can be made to be compatible by just adding supported storage and network controllers. It's difficult to find server-class hardware that isn't supported by ESXi. If you're in a bind, just buy an Intel E1000 network card to complete your installation.