Client in ucmdb terms mean devices that are dynamic (IP's dynamically allocated by dhcp) and should therefor (theoretically) most of the time fail the ICMP sweeps (unless you have a company policy which states all client devices be turned on and connected at certain time of day). So for client ranges discovery should not be dependent on ping sweeps and instead use discovery by Arp Cache reads and use the MAC address rather than IP address.
So for your case, for client ranges, you should maybe look into jobs such as "IP MAC harvesting" or "Call Home" events with UD Agent deployments.
You say you have UD Credentials? Does that mean you have already deployed UD Agents to your client devices?
I am no hp-expert but I think if you must use client IP ranges you have the 2 options of either deploying and using UD Agents on the client devices or to get access to an SNMP enabled device where you can read Arp cache entries.
If you know exactly the IP range of your client devices and if the DHCP lease times are long you may be able to use Datacenter range and run ip sweeps more frequently on this range.. But you should evaluate this..
I would advise you to read the Data flow Management Guide below and also what the online-help in ucmdb says about IP range types.