Hosts with different NICs and vDS

Hello Gentlemen,

I'm currently migrating an ESXi environment from 4.1 to 5.1. The migration involves upgrading all existing servers to vsphere 5.1 and also migrate all VM's from an IBM SAN to a Nimble iSCSI NAS.

As part of the migration, I have migrated the client from a vSS to a vDS. This is because the client would like to use 10 GE links for the production trunks and iscsi.

There will be two cluster tiers: Tier 1 will contain all new HP servers with 2, 10GE  NICs, with 2 10GE ports each. Tier 2 will have the existing (older) IBM hosts which are all using 6, 1GB NICs.

My questions are:

If I have one vDS using 10GE uplinks, can I add the IBM (older) hosts that are using 1GB uplinks?

Are there any considerations or risks in this setup?

How will this affect functions such as vMotion, HA, etc?

Thanks.