Can I use Threads module and invoke a simultaneous ping/snmpwalk to 100 or more devices and raise an alarm if any of the devices do no respond?

Yes, you can. Though it may not be the best way to achieve your goal. For a start, it may be more memory hungry than you would like.

The first thing to get right is that the Thread module is really a defunct implementation from a bygone age. It has recently been aliased to the modern implementation threads, but it is better to use the latter and save confusion.

The second thing to is write a non-threaded program that given a list of the devices, goes through that list one at a time and calls an appropriate function to do either a ping or an SNMPwalk as required. Once you have that working and tested, it will be a lot easier to reason about how make it do some or all of them concurrently.