Q:

Can one Sqlite db support interaction by two server programs all on the raspberry pi

Say you are running two server programs on a single raspberry pi.
Can they both interact with a SQLite db at the same time?
Or seem to be happening at the same time as requests wait for each other to be executed???

A:

Yes, SQLite supports this.
Historically, the concurrency model in SQLite worked like this: 

Readers don't block other readers, and
Writers block all other readers and writers during the short time it takes to write the data.
Transactions use read-after-write verification, which can have some performance implications on spindle hard drives for multiple inserts.

Nowadays the situation is a bit more nuanced.  SQLite Version 3.0.0 introduced a new locking and journaling mechanism designed to improve concurrency over SQLite version 2 and to reduce the writer starvation problem.  SQLite 3 also supports a Write-Ahead Journal.
The upshot is that SQLite is perfectly capable of handling "medium-concurrency" applications; two server processes on a Raspberry Pi would certainly seem to qualify.

