Being fairly new to both AIDE and OSSEC I've been trying to find out if there are any potential conflicts in having them both installed on one host (CentOS 7.5). It seems like they could work as a multi-layered approach, but I haven't been able to find much about running the in tandem. And of course would there be a difference in running them OSSEC locally vs. an agent on the machine with AIDE? Thanks.
I have used AIDE in past and it does only file integrity monitoring. It creates a database when you first install the same, probably mapping hashes along with the respective file names. This comes handy when you want to see any Malware/Program changes which files.
Said that, OSSEC is more superset. Read "AIDE only does file integrity checks. It does not check for rootkits or parse logfiles for suspicious activity, like some other HIDS (such as OSSEC) do." from this site
I don't see any issue with both of them running on same system, but I don't see value in having both unless you find anything which proves OSSEC prone to hash-collision.
To answer the second part of your question, decision of deploying the OSSEC in Manager/Agent mode or standalone mode depends on the requirement. If there are hundreds of hosts, you want centralized management where all the database is stored on server side.