Depends on which link you're talking about, and what you mean by 'NIC teaming'. Assuming it's active/standby...
- 20 servers @ 10Gbps into switch with 10Gbps ports = 1:1 for your local switch (assuming backplane itself is not oversubscribed)
- 200Gbps of servers aggregated into 1 (?) 10Gbps port towards the aggregation switch = 20:1 for the ToR switch to the aggregation layer
Why is the specific "oversubscription" ratio important to you? To effectively design for a setup like this, you'd need to know average throughput, traffic characteristics, destinations (intra-switch vs inter-switch), etc. A server with a 10Gbps link that only does minor DNS requests is a much different traffic consideration than a fileserver or a DB server. What are you trying to accomplish by determining these numbers in particular?