I have a 256mb Nand Phat PS3, thought I would give this a go. I was on Geohot's CFW, so carried out Modmate's instructions and it works fine. (Both OFW and Wutangrza CFW have to installed in recovery mode)
I copied Wipeout HD and played that online, works fine. I tried Nail'd, no luck, but I don't think this was working through Multiman anyway.
I had NFSHP installed on the XMB and that still works online.
Thanks all for your efforts and not bricking my PS3.