1. Is Data Integrity possible or not ?.
Yes, in most cases and may differ in few cases . CA eHealth and CA Spectrum are two different products and does the polling differently and at different poll cycles . CA eHealth reports availability bit differently than compared to CA Spectrum so you might find a bit of difference in the Availability reports when its compared.
Take a look at the below article on how eHealth calculates the availability of a device and availability backfill in CA eHealth might create a bit of confusion if you compare the report with CA Spectrum .
2.How SNMP Poll Work for CA eheath and for CA spectrum?
This is much larger topic, but in short refer to the below topic where there is a good brief explanation on how spectrum actually does polling/fault isolation which might answer most of your questions
spectrum polling mechanism
Coming to CA eHealth there is no single document which talks about in detail about how the polling works , but refer to below two articles for a bit of understanding
What are the steps in the polling cycle?
How does fast polling work in eHealth?
Again CA Spectrum and CA eHealth are two different products which work differently and the information which is collected during a poll by both the products are very different