Can the verb “tend” be followed by a bare infinitive (“tend be” v.s. “tend to be”)?

The OED provides for no such usage. Adapting the examples:

1) Tend can be used with to/towards.

Walter tended to run.

or

Walter tended towards corpulence.

or

... tends towards infinity.

2) Tend can be used with an adverbial:

fire is hot and tends upwards

No dictionary seems to provide for a usage like:

... tend be ...

Verdict: typo or perhaps a written form of informal/idiomatic speech. (The "tend be" form sounds slightly familiar to my ear, like I've heard people saying it; particularly in the form "they do tend be ...".)

In addition to badroit's excellent answer:

Tend be is unplottable on an NGRAM.

If you are unfamiliar with its use, an NGRAM is a search for a word form or string within an entire corpus of literature which can compare its relative prevalence (statistical probability of occurrence). When asking a question of this type, plotting an NGRAM can often help answer your question.

Google Books has an excellent NGRAM viewer. It readily allows you to assess the prevalence of words and phrases within all of Google Books's considerable corpus!

As Edwin Ashworth points out, it is not a perfect tool. Just one more in the arsenal.