1. In TCP probes (SMTP, HTTP, etc.) InterMapper reports an outage because it has failed to establish a connection within 60 (the default) seconds. InterMapper relies on the underlying OS facility to retransmit the SYN/SYN/ACK packets until it works or it has failed multiple times.
The Xserve probes are TCP probes.

Consequently, if InterMapper reports an outage of a TCP-based probe, it has definitively failed. There have been several attempts to start the connection (using the TCP retry algorithm, with exponential backoff, etc.) and it's fair to say that at least one device (InterMapper) has already failed to connect. There's no need to retry again.

2. For UDP probes (Ping, SNMP, etc.) InterMapper sends N requests (default is three attempts) spaced M seconds apart (default is three - both parameters are settable) before declaring the device to be down.

In this case, too, if InterMapper reports an outage, the device has failed to respond to a number of short-interval requests, and there's no additional need to retry.