Short answer, only in small amounts. The pH is very high and can interfere with the composting process. I would recommend a couple of quarts in a cubic yard pile at most.

For more you can search this forum, there are numerous discussions on ashes.

some pellets might have additives and binders that may not be good for the garden.
See if you can find out what they have in them and if it's safe.

It depends on where you live and what your soil pH is.

If you have alkaline soil, adding strongly alkaline ashes is not a good idea. If your soil is aci8dic, they can help lower the pH.

Wood ashes, pellets of logs, are not a good addition to compost, even in small amounts. Wood Ashes should not be spread around the garden unless a good, reliable soil test is done before any application takes place because of the high pH.
You can find a lot of information that does say you can add wood ash to compost by people that have not studied this but from people that have looked closely at the composting process you will be told do not put that wood ash in your compost.