People are still using 10g?!
OHS is part and parcel of fusion middleware, so yes 11.whateverVersion and OHS is what you get.
Why would you not migrate to 12c, do you like not being supported?
And why would you try to put a Frankenstein solution in, what does IHS give you that Oracle does not?
AFAIK you first need to upgrade to 220.127.116.11+ before you can go to 12C, see: https://www.rittmanmead.com/blog/2017/02/obiee-11-1-1-7-is-it-still-supported/
But LFG is right, you've been riding a time bomb by still using 10g and you will be again if you do not upgrade to 12c before Dec-2021
"You first need to upgrade" - well doesn't that depend on your migration strategy, re-implement might be no more work and a cleaner solution...
True, re-implement may be cleaner, depending on what exactly you need to migrate.
OP is talking about upgrade however, so I linked to the Rittman post to help him realize what that will mean for his situation.
Upgrading to 12c is our next milestone but for now we are moving to 18.104.22.168.
In 10g we already have IHS installed, so want to confirm if same configuration I can use for 11g instead of installing OHS which will be one more extar activity I have to do.
I checked in Certification Matrix for 22.214.171.124 and IHS is not mentioned over there.
So is there any doc available where I can check this configuration in 11g, how to connect IHS to weblogic server or its mandatory I have to go with OHS?
No, this is unsupported, there is no document and if you persue this course of action then you invalidate your license agreement and are entirely unsupported.