Yes, this can definitely be done, subject to the policies of the DB scheme holder. I transferred to a UK based Self invested Personal Pension (SIPP). The route you will take largely follows the steps of a UK resident, but there are extra hurdles to clear. (transfers to other schemes such as QROPs, or to US pensions have been debated elsewhere - I have no experience of these, but by reputation: 'Here be Dragons')
Should I transfer out of my UK defined benefit pension (DB) scheme? Think long and hard before doing this, you are swapping a 'guaranteed' future income for a specific cash amount (the transfer value), essentially assuming all risks for managing this cash value to provide for you & yours in retirement
Possible reasons for transferring out (not exhaustive) :

How to report it (to the IRS) (Fair warning: I took no professional advice on this, I think I took a middle of the road approach, but these are just my unqualified opinions)
On form 8938: Assuming you are above the well documented reporting thresholds, you absolutely need to report the DB scheme annually on your tax returns via this form (plus any and all all your overseas accounts) . If you have not been doing this in previous years, suspect you would be seriously pushing your luck by initiating a transfer (for the pedants, perhaps there's an argument that DB pensions are generally declared with zero value, and if this was your only UK asset, then you might avoid declaring, but to then convert it to a SIPP with declarable value and suddenly start reporting it would seem like a high risk strategy)
On FBAR : Again, assuming above thresholds, report the DB scheme and any other foreign accounts via FBAR, If you haven't been doing this annually, forget about transfers and deal with that first

When you transfer to the SIPP, continue reporting via both forms (I entered the old and new names and account numbers in the same section of the form, with the new address).

I took my time (several years) contemplating the transfer out,I got a transfer value several years ago, and yearly thereafter. I reported the transfer value of the Pension as its value on both the 8938 and FBAR (instead of 0, which is typically recommended for DB schemes). My rationale was that this would look less alarming than having a DB pension suddenly switch from a zero value to a large sum. In hindsight, just a naive notion on how the IRS works, I have no idea if this has any bearing. As a side note, my transfer value increased substantially each time I got the quote; I couldn't get details on how these values are calculated, which might have allowed me to optimize transfer timing - just the last offer was one I couldn't refuse.

Form 8833
More controversial, this form allows you to explicitly specify a treaty position (based on the UK-US tax treaty). The argument goes that you may need this form to ensure the transfer between schemes is not treated as a distribution
this is the main substrate I used to decide whether to submit:

On balance it seems unlikely that the form is needed, however, it didn't seem too difficult to fill in: https://www.irs.gov/pub/irs-pdf/f8833.pdf , so I did.
Section 1, I specified article 18, Section 2 (irc's) , I left blank (ran out of time to work out which IRC's apply -if anyone knows, please post), Section 5, I answered no, Section 6, I wrote something to the effect:
'Pension was transferred between UK approved pension schemes' value $xxx reported form 8938, Para 1 of article 18 specifically exempts taxation of pension transfers'

Things I didn't do: declaring a distribution of the pension on my 1040, completing 3520 and 3520-A (these are awful forms, and I've seen no evidence they are required - I worry in fact that completing these forms might complicate my position further by recharacterizing my pension as something else) - again, just my opinion. Cook County posted a PDF earlier in the thread that is a very interesting read; in the end though, it seemed to me most of the cautionary notes therein reflected transactions not covered by a tax treaty (i.e. other countries - not UK/US)

That's about it; hope it helps someone; I'll post if there's ever any follow up for me;