Yes, you should be able to obtain a valid cert from Comodo via the website you specified.
My suggestion would be to go for a GoDaddy Premium SSL certificate. Its alot cheaper, and the application process is quicker. I've already spoken to them regarding vPro provisioning certificates, and they know what they're doing.
The free certificates will not work for vPro provisioning, you need to specify a custom OU value of Intel(R) Client Setup Certificate in your CSR, and the free certs dont allow this.