Definitely not. Dalvrij is only valid in The Netherlands, from or up to the frontier. You can travel to of from Belgium, but you do need to buy an international ticket from a station in The Netherlands to Brussels or vice versa. It is not possible to check in or -out with your ov-chipcard in Belgium.

You can choose for 100 percent reduction in The Netherlands and you only have to pay for the ride from the frontier to Brussels as this is Belgium and not The Netherlands. Do not check in but open the gate with the square Aztec image on your international e-ticket. Take your ov-chipcard with you as this proves that you have Dalvrij and the reduction is valid  

You can buy an e- ticket at NSInternational or B-Europe.com.

Depending on how often you will be commuting, a season ticket for the Belgian part (between the border and Brussels) can be cheaper than single tickets. A season ticket in Belgium is available for 1 month, 3 months, 1 year. There's also a Flex Season Ticket that can be interesting when you commute 2 or 3 days a week. Prices to the border cannot be looked up online but I can look them up later today.

If I have a season ticket for Belgium and the Dal Vrij for the Netherlands, do I need an additional ticket to cross the Belgium/Netherlands border, or are those enough? If there is an additional ticket required, is there a season or multi-ride pass option to save costs? Thank you all so much for your help!

For one more month there is

Additionally you need a ticket Noorderkempen - border, €6,50 one way (or less for the slower route through Roosendaal).